Why are emails from Microsoft accounts being rejected by Gmail, and what is the role of IPv6?

Marketer from Email Geeks shares information about Google (Gmail) rejecting email from Microsoft accounts due to a "domain reputation issue." The issue was specific to Microsoft sending to Gmail via IPv6, with Google detecting these emails as spam to protect their end users. Both Google and Microsoft have acknowledged the issue, and the sender she worked with is now able to deliver to Gmail.

Email marketer from Google Support explains that Gmail might reject emails if the sender is blocked or marked as spam. They advise checking the blocked senders list and ensuring that the sender isn't inadvertently marked as spam.

Email marketer from Microsoft Support Forum responds that Gmail may reject emails from Outlook.com if the IP address or domain has a low reputation due to spam activity. They suggest checking if the Outlook.com account is blocked and reviewing Microsoft's policies to ensure compliance.

Email marketer from StackExchange explains Gmail's spam filters may mark emails from Microsoft accounts as spam due to shared IP addresses and domain reputation. They suggest ensuring proper email authentication (SPF, DKIM, DMARC) is in place, and to monitor sender reputation.

Email marketer from Mailjet shares tips on improving email deliverability to Gmail, including using a dedicated IP address (especially for IPv6), monitoring sender reputation, and implementing proper authentication protocols. They recommend regularly checking Google Postmaster Tools for insights.

Email marketer from SparkPost Blog shares that IPv6 can introduce deliverability challenges if not properly configured. They highlight that many older email systems aren't fully compatible with IPv6, and poor IPv6 reputation can negatively impact delivery rates to Gmail.

Email marketer from DNSQueries advises users to check their SPF (Sender Policy Framework) records to ensure that Microsoft's sending servers are authorized to send email on behalf of their domain. Incorrect or missing SPF records can lead to emails being rejected by Gmail.

Email marketer from MXToolbox explains that poor IP reputation can cause email delivery problems. They recommend using their tools to check IP reputation against various blacklists and implementing email authentication protocols like SPF, DKIM, and DMARC.

Email marketer from Reddit shares that Gmail's aggressive spam filtering can sometimes mistakenly block legitimate emails from Microsoft accounts. This is often due to shared IP addresses used by Microsoft, which can be affected by the behavior of other users. They recommend checking spam folders and contacting Gmail support.

Expert from Spamresource explains that Gmail treats IPv6 reputation differently than IPv4 reputation. Sending from a shared IPv6 address or with poor IPv6 setup can negatively impact deliverability to Gmail. While not impossible, sending email to Gmail over IPv6 requires careful configuration and monitoring.

Expert from Word to the Wise explains that Return Path certification (now Validity) can help improve deliverability to Gmail and other providers, but doesn't solve fundamental sending issues. It acts more like a 'fast pass' once other deliverability issues (authentication, content, list hygiene) are properly addressed.

Expert from Email Geeks suggests that the problem is made worse by people who exploit default DKIM domains/subdomains in G Suite and O365 to avoid damaging their own domain reputation while sending unwanted emails.

Expert from Email Geeks states that Google holds mail over IPv6 to higher standards and that Microsoft customers have sent so much spam to Google that their IP range has a bad reputation. If delivery problems exist from Microsoft or Google and not elsewhere, it is likely an infrastructure reputation problem.

Expert from Email Geeks explains that sending mail to Gmail over IPv6 can lead to problems if not done correctly. He shares a link to an article he published in 2020 about this issue and notes that Google seems to treat reputation differently on IPv6 versus IPv4.

Documentation from RFC Editor details the original SMTP (Simple Mail Transfer Protocol) standards, which govern how email is transmitted across the internet. It outlines basic requirements for message formatting and delivery, though it doesn't specifically address IPv6 or Gmail's filtering practices.

Documentation from Microsoft Docs outlines troubleshooting steps for email delivery issues from Microsoft accounts. It suggests checking sender reputation, ensuring proper DNS configuration, and following Microsoft's sending policies to avoid being flagged as spam by Gmail.

Documentation from Google Postmaster Tools shares that Gmail uses IP reputation and domain reputation to filter spam. Poor IP reputation, potentially due to IPv6 misconfigurations or shared IPs with spammers, can lead to rejection. They recommend monitoring sender reputation and following best practices.

Documentation from RFC Editor describes the current standard for Internet Message Format. It covers aspects like header fields and message structure, important for ensuring that emails are correctly interpreted by receiving servers like Gmail. This does not delve into IPv6 issues.

Documentation from IETF outlines the specifications for IPv6 and its implementation within the Internet Protocol Suite. It is mentioned how IPv6 can affect email deliverability depending on server configurations.