You set up HubSpot, connected your CRM, built your first campaign, and hit send. Then someone on your team opens the email in Gmail and notices something. Right under your name, in grey text: *via hubspot.com* .
It looks like a mass marketing system sent it, because as far as Gmail is concerned, that is exactly what happened.
The “via hubspot.com” label is not a cosmetic issue. It tells the recipient that the email did not come directly from your domain. It means your DKIM is not aligned. And if your domain has a DMARC policy above p=none, some of those emails are already failing authentication quietly in the background, landing in spam or getting bounced before they reach anyone.
Here is what is happening and how to fix it.
When you send marketing emails through HubSpot without connecting your domain, HubSpot sends the email using its own infrastructure and signs it with its own DKIM key. The d= field in the DKIM signature reads hubspot.com, not yourdomain.com.
DMARC alignment requires the domain in the DKIM signature to match the domain in the visible From address. If your email says it comes from marketing@yourcompany.com but the DKIM signature says d=hubspot.com, alignment fails. SPF has the same problem: HubSpot’s servers are sending the mail, and unless your SPF record explicitly includes HubSpot, SPF fails alignment too.
One aligned pass (either SPF or DKIM, matching your From domain) is all DMARC needs. But without connecting your domain to HubSpot, you get neither.
The “via hubspot.com” label is Gmail’s way of showing the mismatch. It appears when the authenticated domain differs from the visible sender. Fix the authentication, and the label disappears.
The fix is domain authentication inside HubSpot. It connects HubSpot’s sending infrastructure to your domain by publishing two CNAME records in your DNS. Once those records are in place, HubSpot signs outgoing emails with a DKIM key tied to your domain, not its own.
In your HubSpot account, go to Settings (the gear icon) and then navigate to Domains & URLs . From there, select Email Sending Domains .
If you have not connected a sending domain yet, you’ll see an option to connect one. Click it.
HubSpot will ask for the domain you want to connect. This is the domain in your From address, for example yourcompany.com.
HubSpot recommends using a subdomain like email.yourcompany.com as your dedicated sending domain rather than the root domain. The reason is practical: if your sending reputation takes a hit (a campaign gets flagged, spam complaints spike), it stays isolated from your main domain’s reputation. It also makes authentication records cleaner to manage. Either approach works for fixing the “via hubspot.com” label, but a dedicated subdomain is the better long-term setup.
HubSpot generates two CNAME records. They look something like this:
smtpapi._domainkey.email.yourcompany.com CNAME smtpapi._domainkey.hubspot.com
s1._domainkey.email.yourcompany.com CNAME s1._domainkey.hubspot.net
(The exact values come from your HubSpot account. Use what HubSpot gives you, not these examples.)
Add both records to your DNS provider. The record names go in the hostname or name field; the CNAME values go in the points-to or target field.
DNS propagation typically takes between 15 minutes and a few hours. Some providers take longer. HubSpot will verify the records automatically.
Once the records have propagated, return to the Email Sending Domains page in HubSpot. The status should show as verified. If it doesn’t verify within an hour, double-check that there are no extra spaces or punctuation in the record values, and that you added both records, not just one.
After verification, HubSpot signs all emails sent from that domain using your DKIM key. The “via hubspot.com” label disappears.
HubSpot handles its own SPF automatically by managing the return-path (envelope sender) domain. You do not need to add include:hubspot.com to your SPF record for HubSpot marketing emails once your domain is connected via DKIM. DKIM alignment alone is sufficient for DMARC to pass.
That said, if your DMARC reports are showing SPF failures from HubSpot alongside the DKIM failures, you can add HubSpot’s SPF include to your existing record:
include:sendgrid.net
Wait, that is SendGrid’s include, not HubSpot’s. HubSpot’s correct SPF include is:
include:_spf.hubspot.com
Add it to your existing SPF TXT record at yourdomain.com. Keep your total SPF lookup chain under 10 DNS lookups or you’ll hit a PermError, which causes SPF to fail entirely. If you’re already close to the limit, focus on getting DKIM aligned first. One aligned pass is all DMARC needs.
If you don’t have a DMARC record yet, publish one at _dmarc.yourdomain.com as a DNS TXT record. Start at p=none so you can monitor traffic without affecting delivery:
v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com;
The rua= tag tells receivers where to send aggregate reports. Those reports are how you’ll see whether HubSpot emails are passing alignment after the CNAME records go in.
If you already have a DMARC record at p=quarantine or p=reject, connecting HubSpot’s domain authentication is more urgent. Emails failing DMARC alignment at those policies are either being moved to spam or rejected outright. The fix is the same, but every send is actively costing you deliverability until you complete it.
Send a test campaign after the CNAME records verify. Open the email in Gmail and click the three dots in the top right, then select “Show original”. Look for the authentication results near the top of the raw headers:
dkim=pass (yourdomain.com)
spf=pass
dmarc=pass
If dkim=pass shows your domain rather than hubspot.com, the alignment is correct. The “via” label will not appear on the sent message.
If you want to check without sending a campaign, most header analysis tools (including the free Header Analyzer in DMARCS) will read the raw headers from a test message and show you exactly which domain signed the DKIM and whether it aligns with the From address.
If your From address uses a subdomain (like news@email.yourcompany.com), your DMARC record at _dmarc.yourcompany.com covers it under relaxed alignment, which is the default. Relaxed alignment allows a subdomain of the organisational domain to satisfy alignment, so email.yourcompany.com aligns with yourcompany.com under p=relaxed.
You do not need a separate DMARC record at _dmarc.email.yourcompany.com unless you want a different policy specifically for that subdomain. For most HubSpot setups, the root domain’s DMARC record covers everything.
Once the CNAME records are verified, the “via hubspot.com” label stops appearing, your DKIM aligns, and your emails pass DMARC correctly. If you want to see all your sending sources (HubSpot, your CRM, your transactional email provider) in one place with live alignment status, the Sending Sources view in DMARCS shows exactly that. It identifies each source by name rather than raw IP, so you can see at a glance which ones are passing and which ones still need work.
Sending a critical business email only to have it bounce back is a major problem. When you look at the bounce details and see the code “550 5.7.26 This mail is unauthenticated,” you are dealing with a strict security block. Google Workspace has actively stopped your message from reaching the recipient.
This error does not mean the Google servers are down. It means your domain name failed a background check.
Google requires every email sender to prove their identity. If your domain is missing specific DNS records, Google will assume your email is fake, forged, or dangerous. To fix this error permanently, you need to configure three security protocols: SPF, DKIM, and DMARC.
Here is the exact technical process to set up these records, pass the Google security checks, and get your emails back into the inbox.
Before making changes, you need to know what you are fixing. Google looks for three things when you click send:
If any of these fail, you get the 550 5.7.26 error. Here is how to configure them correctly.
If your SPF record is broken or missing, your email will fail immediately.
How to avoid common SPF mistakes: You can only have one SPF record. If you have two different TXT records that start with v=spf1 , Google will ignore both of them, and your emails will bounce. If you use a CRM, a marketing tool, or a helpdesk to send emails, you must put them all in the exact same record.
SPF only checks the server. DKIM proves that you own the domain and that the email content was not changed in transit.
DNS changes can take time to process. If Google says the record is not found, wait 15 minutes and click the button again.
Google now strictly requires a DMARC record for bulk senders. If you send more than 5,000 emails a day, skipping this step will guarantee a 550 5.7.26 bounce.
This specific record uses a policy of p=none . This is exactly what you want when starting out. It tells Google that you have DMARC turned on, but it asks Google not to delete any emails if a minor mistake happens while you are setting things up.
Do not guess if you fixed the problem. You can check your work using a free tool provided by Google called the Google Admin Toolbox.
Once the tool shows green checkmarks for authentication, your 550 5.7.26 errors will stop.
Adding that simple p=none DMARC record solves your immediate bounce problem. However, it leaves your business totally unprotected against fraud.
Because the policy is set to “none,” anyone on the internet can still pretend to be you. Spammers can forge your email address, send fake invoices to your clients, and ruin the reputation of your domain. To stop this, you need to change your DMARC policy from “none” to “reject.”
Moving to a reject policy can be highly technical. If you make a mistake, you could accidentally block your own business emails.
This is exactly why you need DMARCs .
DMARCs is a platform built to manage and secure your email domain. We handle the heavy lifting so you do not have to.
Stop email bounces and protect your business reputation from scammers. Visit DMARCs today to get full control over your email security.
Sending emails to clients and partners should be a simple process. However, security filters often get in the way and make email delivery complicated. If your company uses Microsoft 365, you will likely see a specific warning label called High Confidence Phish. This label can cause major headaches, especially when it blocks a real, safe email from a trusted partner or even an internal team member.
Because email security rules are getting stricter every year, understanding how Microsoft Defender makes its filtering choices is very important for your business. This guide will explain exactly what this threat label means, why good emails get caught in the filter, and the exact steps you can take to fix the problem and keep your email flowing.
Every single email that arrives in your Microsoft 365 environment is scanned by Microsoft Defender. The system acts like a digital guard, looking for signs of scams, bad links, or stolen identities. When the system checks an email, it gives it a score and a category.
The label of High Confidence Phish is the most severe category Microsoft can assign. It means the scanning system is completely sure that the message is a dangerous attack designed to steal passwords or trick your users. Microsoft does not apply this label lightly. The system looks for multiple signs of danger at the same time. This might include a link that goes to a known bad website, a sender address that looks fake, or hidden code inside the email body.
When an email gets this label, Microsoft stops treating it like normal spam. It triggers a completely different set of rules designed to keep the email as far away from your users as possible.
You might wonder why a user cannot just go into their Junk folder and save the email themselves. This is due to a Microsoft policy called Secure by Default.
Microsoft decided that some threats are simply too dangerous to leave up to regular employees. If an email is flagged as a High Confidence Phish, the Secure by Default rule takes over. The email is completely blocked from the user’s view. It does not go to the Inbox, and it does not go to the Junk folder. Instead, it gets locked away in a hidden admin quarantine.
Regular users will not even know the email was sent. They cannot see it, and they cannot click a button to release it. Only an IT administrator with the right permissions can log into the security portal, find the blocked email, and decide what to do with it. This rule is great for stopping real attacks, but it creates a big problem when the system makes a mistake and blocks a normal business email.
It is frustrating when a real email gets the worst possible security label. For websites and businesses focused on email delivery, this issue almost always points back to a failure in email authentication.
Email authentication is how a sender proves they are who they say they are. Microsoft looks very closely at three main technical records: SPF, DKIM, and DMARC. Think of these records as a digital ID card for your domain name.
If a partner company sends you an email, but their systems are not properly listed in their own SPF record, Microsoft gets suspicious. If the email is missing a digital signature from DKIM, the filter gets even more suspicious. Finally, if the sender has a broken DMARC setup, Microsoft Defender assumes the sender is a hacker trying to fake an identity.
When poor DMARC records are combined with common business words like “invoice,” “login,” or “urgent request,” the filter easily pushes the email into the High Confidence Phish category. While a bad link can also cause this, missing or broken DMARC records remain the top reason why good emails fail to deliver.
When a safe email is blocked, you need to take action quickly to get the message to your user and teach the system to stop making the same mistake. You must handle this from the admin side.
Find and Release the Blocked Email
Your first step is to log into the main Microsoft Defender portal. You need to look for the quarantine section. Here, you will see a list of all the blocked emails. When you find the safe email that was trapped, you can click a button to release it. This will finally send the message to the user’s normal inbox.
Report the Mistake to Microsoft
Releasing the email is only half of the job. When you release it, the system will ask if you want to report the message as a false positive. You must always say yes to this option. Reporting the email sends a copy back to Microsoft and tells their system that the filter made a mistake. If you skip this step, the filter will not learn, and it will block the next email from that exact same sender.
Sometimes, teaching the filter takes a little bit of time. If you have a trusted partner who sends you emails every day, you cannot wait for Microsoft to update their global system. You need those emails to arrive right now.
To fix this right away, you can use a feature called the Tenant Allow and Block List. When you release an email and report it as a mistake, Microsoft will give you an option to allow that sender. This creates a temporary rule that forces your system to ignore the High Confidence Phish label for that specific sender.
This temporary pass usually lasts for up to thirty days. It acts as a quick bandage. It allows the important business emails to arrive safely while you work with the sender to fix the real technical problems behind the scenes.
Quick fixes are helpful, but the only way to permanently stop these delivery problems is to fix the root cause. This means cleaning up the email authentication records.
If your own company emails are getting blocked, you must look at your DMARC, SPF, and DKIM settings. You need to verify that every single system that sends email for your company is correctly authorized. This includes your main email server, your marketing tools, and your billing software. When all your tools are set up correctly, your DMARC records will align perfectly. Microsoft will trust your emails, and the phishing filter will let them pass.
If an outside partner is getting blocked, you cannot fix it for them. You must contact their IT team and advise them to check their DMARC setup. Good authentication is the absolute best defense against aggressive spam filters.
Dealing with a High Confidence Phish label can feel like a heavy burden, but it is actually a clear sign of how modern email works. Security systems are no longer trusting emails just because they look nice. They require hard, technical proof that the sender is real and safe.
When you see these blocks happening, it is a perfect reminder to audit your own systems. Relying on quick fixes like safe sender lists will not work anymore. Microsoft ignores user-level safe lists when dealing with high-level threats. The only path forward is to embrace strong email rules.
By taking the time to set up strict DMARC policies, you protect your own brand name from being stolen by hackers. You also ensure that your important messages skip the quarantine and land safely in your clients’ inboxes. Paying attention to your email records today will save you countless hours of fixing blocked messages in the future, keeping your daily business operations smooth and secure.
You have spent hours building your WooCommerce store. You sourced the right products, designed a beautiful storefront, and finally started making sales. But almost immediately, a major problem appears. Customers are contacting your support email asking, “Where is my order confirmation?” or “I never got a receipt.”
When you check your WooCommerce dashboard, the orders are there. The system says the emails were sent. So where did they go?
In almost every case, they went straight to the customer’s spam folder, or they were blocked completely by the customer’s email provider.
When your transactional emails fail to reach the inbox, it hurts your business. Customers lose trust in your brand. They worry they have been scammed. Your support team wastes time manually resending receipts and tracking numbers.
The good news is that fixing this issue is straightforward once you understand how email delivery works. This guide will cover exactly why WooCommerce emails go to spam and give you the exact steps to fix the problem permanently.
Before fixing the problem, it helps to understand what kind of emails we are talking about.
Transactional emails are automated messages triggered by a specific action a user takes on your website. They contain information that the user specifically requested or needs to know.
In a WooCommerce store, transactional emails include:
These are very different from marketing emails. Marketing emails are promotional messages sent to a list of subscribers, like newsletters or holiday sale announcements.
Because transactional emails contain critical information, customers expect them to arrive instantly. Email providers like Gmail, Yahoo, and Outlook know this. However, if your website is not sending these emails using the correct technical standards, those providers will treat your critical receipts exactly like junk mail.
There are three main reasons why your online store is failing to reach the inbox. They usually come down to how your website sends the mail, the reputation of your server, and missing security records.
By default, WordPress and WooCommerce use a function called PHP mail() to send emails. This is a basic script that tells your web hosting server to generate an email and push it out to the internet.
The problem with PHP mail() is that it has zero authentication. It is very easy for a spammer to write a PHP script that claims an email is coming from your domain name. Because it is so frequently abused by malicious actors, major email providers are highly suspicious of any message sent this way. Many web hosting companies even disable the PHP mail function entirely to prevent spam from originating on their servers.
If you run your WooCommerce store on a shared hosting plan, you share a single server IP address with hundreds or thousands of other websites.
If just one of those websites gets hacked and starts sending out spam, the IP address for the entire server gets blacklisted. Because your website shares that exact same IP address, email providers will look at your outgoing order confirmations, see the blacklisted IP, and send your emails straight to the spam folder. You are essentially being punished for the bad behavior of your digital neighbors.
This is the most common reason emails fail today. When an email arrives at a Gmail or Yahoo inbox, the receiving server checks the domain name in the “From” address. It then looks up the public records for that domain to see if the server that actually sent the email was authorized to do so.
If you have not set up the correct security records (SPF, DKIM, and DMARC) in your domain settings, the receiving server cannot verify your identity. In the past, this might have resulted in a spam warning. Today, it usually results in the email being rejected entirely.
You cannot ignore email authentication anymore. In early 2024, Google and Yahoo implemented strict new rules for anyone sending emails to their users.
They mandated that senders must properly authenticate their emails. If you do not have SPF, DKIM, and DMARC set up correctly, your emails will be delayed, marked as spam, or completely blocked. While these rules were heavily publicized for bulk senders doing marketing, the authentication requirements apply to anyone sending emails, including small WooCommerce stores sending order receipts.
If your emails are suddenly going to spam when they used to work fine, these new security rules are likely the reason.
To fix your WooCommerce email problem, you need to understand the three pillars of email authentication. These are simply text records that you add to your Domain Name System (DNS) settings.
SPF is a public list of all the servers and services that are allowed to send emails on behalf of your domain name.
Think of it like a guest list at a private event. When an email arrives at a receiving server, that server checks your domain’s SPF record. If the IP address that sent the email is on the list, the email is allowed in. If the IP address is not on the list, the email is treated as an imposter.
If you use a third-party service to send your WooCommerce emails, you must add their specific include statement to your SPF record.
DKIM adds a hidden digital signature to every email your website sends.
This works using a pair of keys. You keep a private key hidden on the server that sends your emails. You publish a public key in your domain’s DNS records. When your server sends an email, it uses the private key to sign the message. When the email arrives, the receiving server uses your public key to verify the signature.
DKIM proves two things. First, it proves that the email really came from you. Second, it proves that the contents of the email were not altered while it was traveling across the internet.
DMARC is the policy that ties SPF and DKIM together. It is a set of instructions you publish in your DNS that tells receiving servers exactly what to do if an email fails the SPF or DKIM checks.
Without DMARC, if an email fails authentication, the receiving server just guesses what to do with it. With DMARC, you are in control.
A DMARC record contains a “policy” (the p= tag) that can be set to three levels:
DMARC also provides reporting. Every day, providers like Google and Yahoo will send XML reports to an email address you specify in your DMARC record. These reports tell you exactly who is sending emails on your behalf and whether those emails are passing or failing authentication.
Because reading raw XML files is incredibly difficult, you need a dedicated DMARC service to process these reports and turn them into readable charts.
Now that you understand the problem, here is the exact process to fix your WooCommerce emails and ensure they land in the inbox every time.
You must stop relying on your web host to send emails. Instead, you need to route your WooCommerce emails through a dedicated Transactional Email Service using SMTP (Simple Mail Transfer Protocol).
These services have massive teams dedicated solely to maintaining high IP reputations and ensuring fast delivery. Good options include:
Sign up for one of these services. Most offer a free tier that is more than enough for a new or growing WooCommerce store.
Once you have an account with a transactional email provider, you need to connect it to your WooCommerce store. You do this using an SMTP plugin.
Now, instead of WordPress trying to send emails directly, it will hand the email data over to your professional email service to deliver.
This is the most important step. Even if you use a great service like SendGrid, your emails will still go to spam if you do not authorize SendGrid in your domain settings.
Log in to the company where you manage your domain name (like GoDaddy, Namecheap, or Cloudflare). You need to navigate to the DNS Management or DNS Records section.
Your transactional email provider will give you specific records to add. Generally, it looks like this:
Add the SPF Record:
You will add a TXT record. If you already have an SPF record for your normal business email (like Google Workspace or Microsoft 365), do not create a second one. You must edit the existing one to include your new service. For example, if you use Google Workspace and add Mailgun, your combined SPF record will look something like this: v=spf1 include:_spf.google.com include:mailgun.org ~all
Add the DKIM Records:
Your email provider will give you specific CNAME or TXT records for DKIM. This usually involves creating a record with a name like selector1._domainkey and pasting a long string of random characters into the value field. Add these exactly as your provider instructs.
Add the DMARC Record:
Create a new TXT record.
*Note: Replace the email address with the reporting address provided by your DMARC management software.*
Do not assume everything is working just because you saved the settings. You must test your configuration.
Go back to your WordPress SMTP plugin settings. There will be an option to send a test email. Send it to an email address you control.
Next, use a free deliverability testing tool. Websites like Mail-Tester.com will give you a temporary email address. Send a test email from your WooCommerce store to that temporary address. The tool will analyze the email and give you a score out of 10. It will tell you exactly if your SPF, DKIM, and DMARC records are configured correctly, and if your server IP is on any blacklists.
If you score anything below a 9/10, review the errors the tool provides and fix your DNS records.
Technical setup is the biggest factor in email deliverability, but the actual content of your emails matters too. Spam filters scan the words and formatting inside your messages.
Keep the Code Clean
WooCommerce provides default templates that are clean and well-coded. If you use a plugin to heavily customize the design of your emails, ensure it does not generate broken HTML. Messy code is a major spam trigger.
Avoid Spam Trigger Words
Even in a transactional email, try to avoid writing things in ALL CAPS. Avoid using multiple exclamation points. Do not include phrases commonly used by spammers, such as “Click here now,” “100% free,” or “Act immediately.”
Include Your Physical Address
Anti-spam laws in many countries require businesses to include a valid physical mailing address in their emails. Ensure your company address is located in the footer of all WooCommerce emails.
Make Subject Lines Clear
The subject line should describe exactly what is inside the email. “Your Order Confirmation from [Store Name]” is perfect. A vague subject line can confuse users and cause them to manually mark the message as spam.
Seeing your WooCommerce emails land in the spam folder is frustrating, but it is a highly solvable technical issue. By abandoning the default WordPress PHP mail function, routing your messages through a professional transactional SMTP service, and strictly enforcing email authentication with SPF, DKIM, and DMARC, you can permanently fix your deliverability problems.
Take the time to configure your DNS records correctly today. Your customers will receive their receipts on time, your support tickets will drop, and your domain reputation will be protected for the future.
Can I just use my free Gmail account to send WooCommerce emails?
You should never use a free @gmail.com or @yahoo.com address as the “From” address for your WooCommerce store. Major email providers have strict DMARC policies on their free domains. If you try to send an email from your website claiming to be a @gmail.com address, Gmail will automatically reject it because your website is not an authorized Google server. Always use a professional domain name, like sales@yourstore.com .
How long does it take for DNS changes to work?
When you add your SPF, DKIM, and DMARC records, the changes do not happen instantly across the globe. It can take anywhere from a few minutes to 48 hours for DNS records to propagate. If your test emails are failing right after you make changes, wait an hour and try again.
Do I need a dedicated IP address for my transactional emails?
For most small to medium WooCommerce stores, a shared IP pool from a reputable provider like Postmark or SendGrid is perfectly fine. These companies actively monitor their shared pools and kick out bad senders. You only need to purchase a dedicated IP address if you are sending hundreds of thousands of emails per month. If you have low sending volume on a dedicated IP, you will actually struggle to build a good sender reputation.
What should I do after my emails are delivering successfully?
Do not forget about DMARC. Remember that you set your DMARC policy to p=none to start. Over the next few weeks, monitor the DMARC reports coming into your management dashboard. Check to ensure all your legitimate WooCommerce emails are passing the checks. Once you are confident everything is authenticating correctly, you should change your DMARC policy to p=quarantine and eventually p=reject . This protects your domain from being spoofed by hackers and further improves your reputation with inbox providers.
Email delivery has quietly shifted from a marketing problem to an infrastructure problem. Good copy and clean design are no longer enough. If your domain is not configured correctly, your emails simply will not reach the inbox. Google and Yahoo made that clear when they rolled out bulk sender requirements in 2024. By 2026, enforcement is strict. The grace period is over. Messages that do not meet these standards no longer face temporary delays. They are now hit with permanent 550 rejection codes or sent directly to the spam folder. There is no grey area anymore.
If your organisation sends newsletters, marketing campaigns, or automated emails at scale, this is not a project to review later. It directly affects revenue, customer communication, and brand trust. This guide breaks down what actually matters, what the new enforcement timeline looks like, and what you need to fix right now.
Who is considered a bulk sender
The rules apply once you cross roughly 5,000 emails in a single day to personal Gmail or Yahoo inboxes. There are a few critical details that catch people off guard.
The count includes your entire domain. If different teams are sending from multiple subdomains, it all adds up to one total. Splitting volume across sales, marketing, and support does not help you bypass the limit.
Once you cross that limit even once, your domain is treated as a bulk sender permanently. Reducing volume later does not reset your status.
The threshold is based on personal inboxes, but the same filtering logic applies across business email environments. In practice, these standards should be applied to all outbound email. The industry has reached a point where baseline standards are identical across Google, Yahoo, and Microsoft.
Authentication is now mandatory, not optional
There are three primary records that define whether your emails are trusted. All three must be correctly configured to pass the security checks.
Sender Policy Framework (SPF)
SPF tells receiving servers which systems are allowed to send email on your behalf. Every platform you use must be listed in a DNS text record. Missing even one service will cause delivery failures. You must also be careful of the strict DNS lookup limit. An SPF record can only require 10 DNS lookups to validate. If you use multiple marketing and sales tools, you can easily exceed this limit, causing the whole record to fail. You must audit and flatten your SPF records to stay within the limit.
DomainKeys Identified Mail (DKIM)
DKIM signs your emails with a hidden cryptographic key. This proves the message has not been altered in transit and genuinely comes from your domain. As of 2026, 2048-bit keys are the required minimum standard. Older 1024-bit keys are no longer considered secure and will be rejected. You must generate new keys in your email sending platforms and update your DNS records.
Domain-based Message Authentication, Reporting, and Conformance (DMARC)
DMARC ties everything together. It tells inbox providers what to do when authentication fails and ensures the visible sender matches what is being verified in the background.
A basic DMARC policy is no longer enough. Monitoring with a policy set to “none” is only a starting point. Moving towards a policy of “quarantine” or “reject” is becoming standard practice to stop domain spoofing. In 2026, the PCI DSS v4.0 regulations also mandate DMARC for organisations handling credit card data, making this a strict compliance requirement for many businesses.
This is also where most teams struggle. DMARC reports are raw XML files that are not readable without processing. Platforms like Dmarcs.com simplify this by turning those reports into clear insights and highlighting unauthorised senders. Using a dedicated tool like Dmarcs.com allows leadership and IT teams to monitor alignment issues and threats without digging through raw code.
Your reputation is measured in complaints
Authentication proves identity. It does not guarantee inbox placement. Inbox providers track how users react to your emails. The most important signal is the spam complaint rate.
The expectations are incredibly tight. You should aim to stay below 0.10 percent. That is one complaint per one thousand emails.
If you reach 0.30 percent, filtering becomes aggressive. Emails start landing in spam consistently, and recovery becomes difficult. If you cross this threshold, Google removes your access to delivery mitigation support. Support channels will not prioritise your case or help you lift blocks until your metrics drop below 0.30 percent for seven consecutive days.
To track this properly, you need to rely on Google Postmaster Tools and the Yahoo Complaint Feedback Loop. Marketing platforms do not have visibility into what users report directly inside their inbox. You must set up these native provider tools to get accurate data.
Unsubscribing must be instant and visible
Hiding the unsubscribe link is no longer acceptable. Google and Yahoo require a one-click unsubscribe mechanism built directly into the email header, following the RFC 8058 standard. This creates a visible, native unsubscribe button in the inbox interface, right next to the sender name.
When a user clicks it, it sends an automatic POST request to your server. They should be removed without friction. No login pages, no preference centres, no delays.
There is also a strict deadline. Requests must be processed within two days. Failing to honour these requests within 48 hours will trigger immediate spam filtering.
Transactional emails are excluded, but only if they remain purely transactional. Password resets and order receipts do not need this header. However, the moment you add promotional content to a receipt, the same rules apply.
Technical setup still matters
Beyond authentication and complaints, there are a few technical checks that cannot be ignored.
TLS Encryption
Emails must be sent over encrypted connections using Transport Layer Security. Without it, messages are flagged as insecure, and many providers will reject them outright.
Forward and Reverse DNS
Your sending IP addresses must have proper forward and reverse DNS records. The reverse DNS lookup must point to a hostname that matches your forward DNS domain. If the domain and IP do not align, it raises suspicion immediately and guarantees a high spam score.
RFC 5322 Formatting
Email formatting must follow strict standard specifications. Using free email addresses like Gmail in the sender field, or having inconsistent or duplicate headers, will cause failures. The sender address must belong to the domain you own and control.
Poor list quality will damage your domain
High bounce rates signal bad sending behaviour. If too many emails are sent to invalid addresses, inbox providers assume the list is not clean or was acquired improperly. You should keep bounce rates below 2 percent. Anything above 5 percent starts to damage your reputation significantly, leading to account suspensions from email service providers and domain blacklists.
This comes down to strict discipline. Use a double opt-in process for new users. Validate existing lists using list cleaning software before sending large campaigns. Remove inactive users regularly. Sending to disengaged audiences reduces your overall engagement metrics, which also affects deliverability.
Protect your main domain
One mistake can impact your entire organisation. If marketing campaigns, cold outreach, and transactional emails all use the same domain, any spike in complaints will affect everything. Even critical emails like invoices, system alerts, or password resets can end up in spam.
The safer approach is isolation. Use dedicated domains or subdomains for different types of traffic. Keep your core domain reserved strictly for internal and business-critical communication. Register separate, brand-adjacent domains for cold outbound sales. This isolates risk and protects essential operations from marketing mistakes.
What you actually need to check
If you want a practical way to approach this, focus on these essential steps.
The Reality of Continuous Compliance
The rules set by Google and Yahoo are not hurdles to clear once and forget. They are the permanent reality of modern email infrastructure. As your business grows, marketing teams will add new software, sales teams will test new outreach tools, and your sending environment will change. Each of these changes can break your SPF limits or misalign your DMARC records in the background, causing sudden delivery drops.
This is exactly why DMARCS exists. We remove the hard work from email security and give you clear control over your domain. Instead of guessing why emails fail or trying to read confusing XML reports, DMARCS turns your data into simple steps. You can protect your domain, block unauthorized senders, and make sure your emails reach the inbox. You do not need a large IT team to manage this. Take control of your email delivery today with DMARCS.
If you are currently looking at a 550 5.7.1 Sender Authentication Failure Non-Delivery Report (NDR) in Office 365, you are likely dealing with a high-pressure situation. Your outbound emails are hard bouncing. Whether these are critical executive communications, customer invoices, or automated system alerts, they are not reaching their destinations.
We know that blindly adjusting Exchange connectors or guessing at DNS TXT records can easily cause a wider mail routing outage.
The strict deliverability rules enforced by Microsoft, Google, and Yahoo, the 5.7.1 error is rarely a temporary network glitch. It is a hard block. It indicates that Microsoft’s servers, or the receiving external server, do not trust that the email actually originated from your authorized infrastructure.
The code “550 5.7.1” is a blanket SMTP response indicating a permanent access denial. However, Exchange Online appends specific text to the end of this code depending on the exact nature of the failure. You must read the full NDR to understand the context.
Look for these four common variations:
Do not rely solely on forwarded error messages from end users. You need to review the raw transaction logs to understand exactly which server rejected the connection and why.
Systems administrators rely on the command line because the graphical interface often abstracts or hides critical data. We will use the Get-MessageTrace and Get-MessageTraceDetail cmdlets to pinpoint the exact failure point.
First, connect to Exchange Online:
PowerShell
Connect-ExchangeOnline -UserPrincipalName admin@yourdomain.com
Next, run a trace for the specific user experiencing the bounce over the last 48 hours:
Get-MessageTrace -SenderAddress “problem.user@company.com” -StartDate (Get-Date).AddDays(-2) -EndDate (Get-Date) | Select-Object Received, SenderAddress, RecipientAddress, Subject, Status, MessageTraceId
Locate the email that shows a Status of Failed. Copy the MessageTraceId (the long GUID string) and the RecipientAddress . Now, drill down into the exact SMTP transaction events:
PowerShell
Get-MessageTraceDetail -MessageTraceId <Paste-GUID-Here> -RecipientAddress <Paste-Recipient-Here> | Select-Object Date, Event, Action, Detail
The Detail column will output the exact filter or connector that terminated the connection. If you see a failure related to Anti-Spoofing or Authentication-Results, you are dealing with a DNS alignment issue.
If you prefer a graphical interface or need to export a CSV file to share with management, you can use the Extended Message Trace feature.
Once the trace completes, download the resulting CSV file. You are looking specifically for the Authentication-Results column. If you see spf=fail , dkim=fail , or dmarc=fail , proceed immediately to Root Cause 1.
Microsoft Defender for Office 365 has removed all leniency for poorly authenticated mail. If a third-party CRM like Salesforce or an email marketing tool like Mailchimp sends an email using your corporate domain, but you have not explicitly authorized their servers in your DNS, Exchange will block it with a 5.7.1 error.
You must ensure your Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) are properly aligned with your domain.
If your record looks similar to v=spf1 include:spf.protection.outlook.com include:servers.mcsv.net include:_spf.salesforce.com ~all , you might be hitting this limit. When you exceed 10 lookups, a silent PermError occurs. When SPF fails this way, the 5.7.1 block often follows.
To fix this, you must flatten your SPF record by replacing include: statements with explicit IP addresses using the ip4: tag, or utilize an automated dynamic SPF flattening service.
If your NDR contains the specific 550 5.7.1 Unable to relay variant, your problem is not related to DNS. Your problem lies within an Exchange Inbound Connector.
This issue almost exclusively occurs when an on-premises web server, an ERP system, or a network scanner is attempting to route mail through Microsoft 365, but the connector is incorrectly configured. Exchange assumes this is an unauthorized open relay attempt and immediately drops the connection.
Microsoft enforces aggressive outbound spam policies to prevent compromised corporate accounts from turning Exchange Online into a botnet.
If a user’s credentials are breached, or if an employee attempts to send thousands of emails from their personal Outlook client instead of using a dedicated marketing platform, Microsoft will instantly throttle and restrict the account. Every subsequent email they attempt to send will bounce with a 5.7.1 error.
You must manually investigate and unblock the restricted user.
Critical Security Action: Do not simply click Unblock and move on. You must assume the account has been compromised until proven otherwise.
If your error log contains the string S3150 or S3140, you are facing the most difficult 5.7.1 variant to resolve.
Microsoft has placed your IP address on an internal blocklist. If you are using a shared IP pool, which is common on cheaper email marketing tiers, another company in that pool may have ruined the shared reputation. If you are on a dedicated IP, your domain has been flagged for generating high spam complaints or operating without a valid reverse DNS (rDNS) record.
You cannot fix a reputation block with a PowerShell script or a quick settings toggle. You must prove to Microsoft that you are a legitimate, responsible sender.
Microsoft’s initial response to mitigation requests is almost always an automated denial. You must reply to the automated email and politely request an escalation to a human deliverability engineer for manual review.
Resolving the 5.7.1 error today gets your critical business communications flowing again, but it is only a temporary fix if your organization lacks continuous visibility into your email infrastructure. Blindly adding IP addresses to Exchange connectors or managing complex SPF records manually is exactly how enterprises accidentally expose themselves to domain spoofing, phishing attacks, and inevitable future blacklisting.
IT teams need to know exactly who is sending emails on behalf of the company, which IP addresses are failing authentication protocols, and how to transition to a strict enforcement policy without breaking legitimate communications.
This is where a dedicated solution becomes necessary. By implementing DMARCS.COM, you can stop deciphering raw XML files and PowerShell outputs. Once you add our reporting tag to your DNS, the DMARCS.COM dashboard translates complex aggregate reports from Microsoft, Google, and Yahoo into a clear visual map of your entire email ecosystem.
You can instantly identify unauthorized shadow IT tools, monitor your authentication health in real time, and utilize our Enforcement Wizard to safely guide your domain to a strict p=reject policy. Secure your corporate domain, protect your brand reputation, and eliminate the guesswork of email authentication troubleshooting.
As of May 5, 2025, Microsoft has started enforcing strict email authentication rules for domains that send more than 5,000 messages per day to its consumer email services, including Outlook.com, Hotmail.com, and Live.com.
If your emails are not properly authenticated using SPF, DKIM, and DMARC, they are now being diverted to junk folders or rejected entirely. This is not a policy you can opt out of. It is now part of how Microsoft handles email at the infrastructure level.
For organisations that have not kept pace with modern email authentication, this change has already started affecting deliverability, brand trust, and visibility.
If you are still catching up, DMARCS is built to make that process faster, easier, and more reliable.
Microsoft is enforcing three authentication checks, all of which must align with the visible “From” domain. These are verified at the DNS level.
SPF specifies which IP addresses or mail servers are authorised to send email on behalf of your domain.
Purpose : Prevents unauthorised parties from spoofing your domain.
Example DNS record :
v=spf1 ip4:192.0.2.1 include:_spf.example.com -all
DKIM uses cryptographic signatures to confirm that the message has not been tampered with and was sent by an authorised server.
Purpose : Protects message integrity and authenticates the sender.
Example DNS record :
selector._domainkey.example.com IN TXT “v=DKIM1; k=rsa; p=MIGfMA…”
DMARC tells receiving servers what to do when SPF or DKIM fail. It also ensures the visible sender address aligns with the domain used for authentication.
Purpose : Enables policy enforcement, blocks spoofing, and provides reporting.
Minimum DNS entry :
_dmarc.example.com IN TXT “v=DMARC1; p=none; rua=mailto:abuse@example.com”
If your organisation sends over 5,000 emails daily to Microsoft consumer inboxes, you are in scope. This includes:
Even if you primarily send to business addresses, any overlap with Outlook.com or Hotmail.com users will impact your deliverability.
Since the policy took effect:
550 5.7.515 Access denied, sending domain does not meet the required authentication level
Unauthenticated domains are also more vulnerable to phishing and spoofing. Attackers can impersonate your brand, putting both your users and your reputation at risk.
Phishing is still the most widely used method to breach organisations. Most of these attacks rely on forged sender identities.
By enforcing SPF, DKIM, and DMARC, Microsoft is following Google and Yahoo in making domain-level email authentication mandatory. This change:
This is not about new features. It is about enforcing long-standing security standards that many senders have neglected.
Phishing is still the most widely used method to breach organisations. Most of these attacks rely on forged sender identities.
By enforcing SPF, DKIM, and DMARC, Microsoft is following Google and Yahoo in making domain-level email authentication mandatory. This change:
This is not about new features. It is about enforcing long-standing security standards that many senders have neglected.
If you are not compliant yet, take the following steps:
DMARC works only when your domain’s SPF or DKIM is aligned with your visible sender address. Both are recommended for maximum protection.
Managing SPF, DKIM, and DMARC manually is time-consuming and error-prone, especially across multiple sending systems. DMARCS is designed to simplify the process.
With DMARCS , you can:
Our platform is built for scale and visibility, giving you full control over your domain’s email security posture.
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