I had a client having an issue with their emails being blocked by recipients who utilized Microsoft 365 email services.

The client would send an email to some of their customers, and the email would bounce back with an error.

Typically when talking about email blocks, the first thing that comes to mind is an IP address block from an RBL (Real-Time Blacklist) or a temporary block because of a bad actor sending a bunch of unsolicited emails.

However, in this case, it was a content block due to a specific domain name being used in the client’s email. The domain name that was blocked was the company domain name. The same domain name is used to send an email.

Trying to reach out to Microsoft 365 Support when you’re not a custom, hopeless. So I had to purchase a Microsoft 365 account and have the client send me an email, it would get blocked, and then I could reach out to Microsoft 365 Support.

From there, I battled back and forth with Microsoft 365 Support, and they eventually found the domain name in a private block list. They removed it, and there was peace on earth 🙂

I replied to a user’s post in the Microsoft Tech Community forum, providing some of my experience so others could benefit. You can read it here.

Outgoing emails marked as SPAM and Phishing emails by O365 servers

I took some screenshots in case it gets taken down. I’ve linked to the images directly due to their size.