Summary
Even with proper email authentication (SPF, DKIM, DMARC), Outlook/Hotmail may mark emails as 'Unverified Sender' due to several factors that go beyond mere authentication protocols. These include sender reputation, content triggering spam filters, potential issues with Microsoft's systems, or even the possibility of a recently deployed and potentially broken feature by Microsoft. Maintaining a clean email list, properly warming up IPs/domains, avoiding spam trigger words, continuously testing email configurations, and monitoring sending patterns are all vital. Furthermore, transient DNS issues, user complaints, and other complex factors considered by Microsoft’s algorithms can also play a role.
Key findings
- Authentication Incompleteness: Passing SPF, DKIM, and DMARC does not guarantee emails won't be marked as 'Unverified'.
- Reputation Importance: Low sender reputation, especially for new IPs/domains, can trigger the 'Unverified Sender' flag.
- Content Impact: Email content that resembles spam can lead to emails being marked as 'Unverified'.
- Microsoft-Specific Factors: Temporary glitches or newly deployed but problematic features by Microsoft can cause these issues.
- Holistic Assessment: Microsoft's algorithms consider various signals beyond authentication, including user complaints and sending patterns.
Key considerations
- Monitor Reputation: Regularly check sender reputation to identify and address issues promptly, using tools like Google Postmaster Tools.
- Warm-Up Strategy: Implement a proper warm-up strategy for new IPs and domains, gradually increasing email volume to build a positive reputation.
- List Hygiene: Maintain a clean and engaged email list to improve sender reputation and minimize spam complaints.
- Thorough Testing: Test emails using various tools to identify and fix potential deliverability problems before sending them to subscribers.
- Content Optimization: Optimize email content to avoid spam trigger words and ensure relevance to subscribers.
- Policy Implementation: Implement a DMARC policy in DNS records to specify how receivers should handle unauthenticated messages.
- Transient Issues: Be aware that transient issues, like DNS propagation delays or temporary glitches on Microsoft’s side, can also contribute.
- Microsoft Feature Rollout: If a new Microsoft feature is suspected, consider waiting to see if issues are resolved on Microsoft's end before investing significant troubleshooting efforts.
What email marketers say
9 marketer opinions
Even with proper email authentication (SPF, DKIM, DMARC), Outlook/Hotmail may mark emails as 'Unverified Sender' due to several factors. These include: issues with sender reputation (especially for new IPs/domains), content triggering spam filters, temporary Microsoft issues, or even just an indicator to the user that the email is deemed to be suspicious. Maintaining a clean email list, warming up IPs correctly, avoiding spam trigger words, and continuous testing are crucial for avoiding this issue.
Key opinions
- Authentication isn't everything: Passing SPF, DKIM, and DMARC does not guarantee emails won't be marked as 'Unverified'.
- Sender reputation matters: Low sender reputation, especially for new IPs/domains, can trigger the 'Unverified Sender' flag.
- Content can be a factor: Email content that resembles spam can lead to emails being marked as 'Unverified'.
- Microsoft's issues: Issues in Microsoft's systems might cause the behaviour.
Key considerations
- Monitor your reputation: Regularly check sender reputation to catch and address issues promptly.
- Warm-up IP/domain: Implement a proper warm-up strategy for new IPs and domains to build reputation gradually.
- Clean your lists: Maintain a clean and engaged email list to improve sender reputation.
- Test thoroughly: Test emails using various tools to identify and fix potential deliverability problems before sending.
- Content: Clean your content to not appear as Spam
Marketer view
Email marketer from EmailToolTester shares that to avoid spam filters, including those that might cause an email to be marked as 'Unverified Sender', you should ensure your sender reputation is high. Also you should clean your email list, avoid spam trigger words, ensure your content is relevant, and also you should test your email before sending it to large lists.
7 Dec 2021 - EmailToolTester
Marketer view
Email marketer from Reddit suggests that Outlook often marks emails as 'Unverified Sender' because of issues with the sender's domain reputation or because the email content triggers spam filters, even if authentication (SPF, DKIM, DMARC) is properly configured.
24 Dec 2023 - Reddit
What the experts say
3 expert opinions
Even with proper authentication (SPF, DKIM), Microsoft may mark emails as 'Unverified' due to factors such as a broken Microsoft feature, content reputation, sending patterns, user complaints, or general list hygiene. In essence, Microsoft's algorithms factor in a range of signals and even a few negative ones could cause this problem.
Key opinions
- Microsoft Feature Issue: The 'Unverified Sender' mark may be due to a newly deployed and broken Microsoft feature.
- Beyond Authentication: Microsoft considers factors beyond authentication, such as content reputation, sending patterns, and user complaints.
- Poor List Hygiene: Microsoft is now using unverified domain icons, even when SPF and DKIM is setup correctly. This can be resolved by list hygiene to improve sender reputation with real people.
Key considerations
- Wait and See: If a new Microsoft feature is suspected, wait a week or so for them to fix it before intensive troubleshooting.
- Monitor Signals: Monitor content reputation, sending patterns, and user complaints to identify negative signals.
- Improve List Hygiene: Improve list hygiene to improve sender reputation.
Expert view
Expert from Word to the Wise explains that Microsoft may mark authenticated emails as 'Unverified' due to factors beyond authentication, such as content reputation, sending patterns, or user complaints. Microsoft's algorithms consider numerous signals, and even a small number of negative signals can impact deliverability and verification status.
20 Aug 2023 - Word to the Wise
Expert view
Expert from Word to the Wise explains Microsoft is now using unverified domain icons even when SPF and DKIM is setup correctly. She suggests that your best defence to this is list hygiene to improve sender reputation with real people.
8 Dec 2022 - Word to the Wise
What the documentation says
6 technical articles
Even with proper authentication (SPF, DKIM, DMARC), Outlook/Hotmail may mark emails as 'Unverified Sender' because of several factors. The 'Unverified Sender' mark is designed to alert users to potentially suspicious messages, and other factors can trigger the warning. Ensuring that SPF, DKIM, and DMARC records are correctly configured, you should also ensure your sending domain and IPs are not blacklisted. Implement DMARC correctly involves publishing a DMARC policy in your DNS records that specifies how receivers should treat unauthenticated messages. Maintain a clean sending infrastructure and monitor your domain and IP reputation using tools like Google Postmaster Tools.
Key findings
- Suspicious Messages: The 'Unverified Sender' mark in Outlook is designed to alert users to potentially suspicious messages.
- Not Just Authentication: Even with proper authentication, other factors can trigger the 'Unverified Sender' warning.
- Importance of SPF: Invalid or incorrect SPF records will almost certainly cause deliverability issues.
- Importance of DMARC: Implementing DMARC correctly helps prevent email spoofing and phishing attacks.
- Importance of reputation: Ensure your sending domain and IPs are not blacklisted and you are monitoring your domain and IP reputation.
Key considerations
- Check Authentication Records: Ensure that SPF, DKIM, and DMARC records are correctly configured and valid.
- Monitor Reputation: Monitor your domain and IP reputation using tools like Google Postmaster Tools.
- Implement DMARC Policy: Publish a DMARC policy in your DNS records to specify how receivers should treat unauthenticated messages.
- Maintain Clean Infrastructure: Maintain a clean sending infrastructure for positive deliverability.
Technical article
Documentation from Microsoft indicates that emails can be marked as unverified due to missing or invalid SPF, DKIM, or DMARC records. They recommend ensuring that these records are correctly configured and that the sending domain has a good reputation. Transient issues with DNS propagation or temporary glitches on Microsoft's side could also contribute.
10 Mar 2025 - Microsoft Support
Technical article
Documentation from RFC describes how to properly configure SPF records to ensure that sending mail servers are authorized to send email on behalf of your domain. Having an invalid or incorrect SPF record will almost certainly cause deliverability issues.
26 Aug 2024 - RFC-Editor
Can AMP code in emails cause increased spam placement in Outlook and Hotmail, even if they don't render AMP?
Can the sender name impact email delivery to spam in Hotmail/Outlook?
How can I improve email deliverability with Microsoft and avoid spam filters?
How do I get my emails out of spam for Hotmail and Outlook?
How to fix Hotmail/Outlook emails landing in spam even with proper authentication and opt-in?
Why are authenticated emails going to junk in Microsoft Outlook?
