Why are my emails to Microsoft domains being blocked and how can I resolve it?

Email marketer from Reddit explains that emails are getting flagged due to aggressive filtering by Microsoft and encourages senders to follow best practices, monitor their reputation, and use feedback loops.

Email marketer from Web Hosting Talk shares that they had experienced issues when sending HTML formatted emails to Outlook. They solved this by changing the email format from HTML to plain text.

Email marketer from GMass shares that your email can get blocked by Outlook due to too many recipients in a single email, too many emails sent in a short period, or sending to invalid email addresses.

Marketer from Email Geeks advises escalating the ticket with Microsoft and explaining that the domain is not listed, after confirming caching issues are rare.

Email marketer from EmailToolTester explains that to fix deliverability with Microsoft you must set up authentication (SPF, DKIM, DMARC), monitor your sender reputation via SNDS and JMRP and ensure your content adheres to their guidelines. Consistent email volume is also important.

Email marketer from Reddit explains that Hotmail is notorious for blocking IPs if they detect any spam-like behavior. Ensuring proper email authentication and maintaining a clean sending reputation are critical. If you are new IP/Domain you have to 'warm it up'.

Marketer from Email Geeks suggests that if the problem is only occurring when sending to Microsoft, the issue is likely specific to them and offers to check the domains.

Marketer from Email Geeks suggests the issue could be a caching problem where the domain was previously listed but has since been delisted, but Microsoft might still be using cached data.

Email marketer from Mailjet shares that strategies to improve your deliverability include authenticating email with SPF, DKIM and DMARC. Also clean your lists regularly to remove inactive users and monitor feedback loops to understand deliverability issues.

Marketer from Email Geeks explains that the SMTP response indicates the HELO domain is listed in SpamHaus, and Microsoft support is not needed.

Email marketer from SparkPost shares that Microsoft could be blocking your emails because of poor IP/domain reputation, high spam complaint rates, low engagement, or authentication issues.

Marketer from Email Geeks shares that nothing has ever been listed, the reputation of IPs and domains are all good and there are no issues. She also says that if this is only happening with MS it is suggestive of an issue on their side but it is hard to get them to admit it.

Email marketer from Digital Ocean explains that it's important to check IP address against blacklists, set a valid hostname, use a dedicated IP address, and use double opt-in to improve deliverability. Also important to be aware of sending reputation.

Email marketer from Sendgrid shares that emails can go to the junk folder because of factors like spam triggers in the content, lack of authentication, low sender reputation, and recipient engagement.

Expert from Email Geeks shares that you need to be persistent, use small words, make a clear ask and you can usually find someone who will help. You just need to be persistent and keep asking the same thing over and over.

Expert from Spam Resource explains that Microsoft provides SNDS (Smart Network Data Services) which is a free service that helps monitor sending IP reputation. It provides data to help diagnose deliverability issues specific to Microsoft.

Expert from Email Geeks states that Microsoft seems to have just decided email is not important. She also added that she is pointing out to Microsoft that their mail system is currently mailing out duplicate messages 12 hours apart and that it's a trainwreck for email over there.

Expert from Email Geeks explains that "if even Microsoft can't make their filters put their mail in the inbox ... ain't no one gonna do it".

Expert from Word to the Wise addresses the challenges of Microsoft deliverability. They recommend using Microsoft's SNDS and JMRP programs to monitor your sending reputation and understand if your emails are being marked as spam. Also keep in mind that Microsoft's filtering is constantly evolving, so staying vigilant is crucial.

Expert from Email Geeks shares that he's seen the issue from MS before, sometimes it resolves in a couple hours, other times help is needed to nudge them to look into it.

Expert from Spam Resource notes that Microsoft email filtering can be strict, and senders need to follow all best practices, including authentication, list hygiene, and engaging content. Sender reputation is key.

Expert from Email Geeks shares that Outlook has a long history of junking other MSFT mail and there is a lot of history on why.

Expert from Email Geeks suggests filing a ticket and pointing out that you've talked to Spamhaus and the error message appears to be incorrect.

Documentation from Microsoft Support explains that emails might be blocked by Outlook.com due to sender IP address being blocked, reported as spam by users, or due to content filtering if the email is considered spam-like.

Documentation from Microsoft JMRP explains that the Junk Mail Reporting Program (JMRP) helps you monitor when Outlook.com users mark your email as junk, allowing you to identify and address potential issues.

Documentation from Microsoft SNDS explains that using the Smart Network Data Services (SNDS) program you can monitor the health and reputation of your sending IP addresses with Microsoft, and provides data about spam complaints.