How can I tell why I'm not receiving mail in Microsoft 365?

With Microsoft 365 there is an additional place to check for quarantined e-mail. With this e-mail hosting configuration there are three places where an e-mail can get junked or quarantined, that align with the steps of e-mail delivery.

1. During the server-to-server exchange. The e-mail sender will receive a Delivery Status Notification (DSN) if a message is blocked.
2. During the internal Microsoft 365 Defender analysis. No notifications will be sent.
3. During the final mail client delivery. The message may be placed in the Junk folder.

In steps (1) and (3) either the sender or recipient has the ability to check to see if the e-mail was blocked or placed in the Junk folder, but with step (2) there is no notification.

If you are using Microsoft 365 it is important that someone regularly checks your *Microsoft 365 Quarantine*, as follows.

1. Go to: https://security.microsoft.com/quarantine
2. Review the quarantined e-mails, selecting e-mails that should be released.
3. Click "Release".
4. If available, choose "Allow sender".
5. Once released, future emails should arrive in your inbox.

-- David Rutherford