New Outlook rules take effect today & Microsoft will begin rejecting / bouncing emails from domains that lack proper authentication. If your domain isn’t set up with SPF, DKIM, and DMARC, your emails may not reach any Outlook, Hotmail, or Live users.

This is especially critical for anyone sending emails to more than 5,000 recipients at once.

Initially, Microsoft announced that unauthenticated emails would be filtered into spam. However, last week they changed course and decided to enforce rejections right from the start.

As a result, many companies will likely see more rejected / bounced emails, flagged with the 550 5.7.515 error code

.Whatever system you use for mail distribution, make sure your domain is properly authenticated with their infrastructure. Even if you think it is, it's worth double-checking the authentication settings and analyzing your DMARC reports from the past month to ensure all existing mail streams are properly configured.