Why am I suddenly seeing an increase in bounces from Microsoft domains?
Summary
What email marketers say13Marketer opinions
Marketer from Email Geeks agrees with submitting a mitigation request and emphasizes the importance of following up with Microsoft multiple times.
Email marketer from Digital Marketing Forum states that a compromised account may lead to unusual sending patterns triggering Microsoft's spam filters. Suggests auditing account security and user permissions.
Email marketer from Microsoft Support explains that a sudden increase in bounces from Microsoft domains can be due to several reasons including: IP reputation issues, sudden changes in sending volume, content filtering triggering spam filters, or authentication problems (SPF, DKIM, DMARC) not being properly configured.
Email marketer from Litmus explains that Microsoft might be using blocklists that aren't publicly available, causing bounces. Suggests using tools that provide insight into Microsoft-specific deliverability issues and contacting Microsoft support for clarification.
Marketer from Email Geeks suggests that the issue might be with Microsoft's algorithms or filtering criteria. Recommends submitting mitigation requests.
Email marketer from EmailOnAcid Blog shares that Microsoft's Outlook.com is very strict with their spam filters and that temporary issues in their algorithms might cause sudden bounce rate increases. Recommends contacting Microsoft support to address the problem.
Email marketer from Sendgrid suggests looking into content related issues. If you're using URL shorteners in your email copy or tracking links. These could be flagged by Microsoft's spam filters. Try A/B testing emails without those, but changing them to full URL's and removing tracking.
Email marketer from Mailjet explains that it might be an Microsoft-specific algorithm change, or an overzealous application of spam filtering. Contact Microsoft through the appropriate channels with your IP information and a request for them to look into it.
Email marketer from Reddit user u/EmailGuru suggests checking if your IP address has been blacklisted by Microsoft. They also mention that Microsoft's spam filters can be particularly sensitive to sudden changes in email content or subject lines, even in transactional emails.
Marketer from Email Geeks suggests that a change in sending volume could be the issue, as Microsoft is sensitive to volume changes. Also recommends checking email metrics and postmaster/reputation sites and ensuring no compromise in the funnel.
Email marketer from Quora explains that Microsoft may have tightened its spam filtering rules, particularly if you're sending from a new IP address or domain. Gradually increasing your sending volume ('warming up' your IP) can help improve deliverability.
Marketer from Email Geeks, considering the good metrics and SNDS data, recommends asking Microsoft about the issue after mitigation.
Email marketer from StackOverflow explains that Microsoft often uses 'rate limiting' due to IP reputation, which can result in temporary bounces. They suggest checking your Sender Score and ensuring your sending practices are compliant with Microsoft's guidelines.
What the experts say3Expert opinions
Expert from Word to the Wise (Laura Atkins) responds that Microsoft's filtering is heavily influenced by user engagement, and sudden drops in engagement (opens, clicks) can lead to increased bounces. Ensure your emails are relevant and targeted to maintain positive engagement.
Expert from Spam Resource (Steve Linford) explains that sudden bounce increases from Microsoft can indicate issues with IP reputation, and suggests monitoring blocklist status and Microsoft's SNDS tool to identify and address potential problems.
Expert from Word to the Wise (Dennis Dayman) shares that Microsoft has sophisticated spam filtering, and a sudden increase in bounces can be triggered by changes in your sending patterns or content. Audit your sending practices, review recent email campaigns, and ensure alignment with Microsoft's best practices.
What the documentation says4Technical articles
Documentation from DMARC.org explains if your DMARC policy is set to reject emails (p=reject), Microsoft may be rejecting emails that fail SPF or DKIM checks, leading to bounces. Review DMARC reports to identify authentication failures.
Documentation from Microsoft Postmaster outlines best practices for sending emails to Outlook.com and Hotmail. It notes that failure to adhere to these guidelines can result in deliverability issues, including increased bounces. They detail specific IP requirements for reputation.
Documentation from Microsoft SNDS (Smart Network Data Services) explains that it provides data about your IP reputation with Microsoft. A sudden dip in reputation can lead to increased bounces. Reviewing SNDS data can give insights on complaint rates and spam trap hits.
Documentation from RFC on SMTP error codes describes that bounce messages with specific SMTP error codes from Microsoft domains can indicate the reason for the bounce, such as '451 4.7.0 Temporary server error' (often rate limiting) or '550 5.7.1' (general rejection due to spam filtering).