Cannot receive mail from other Microsoft 365 tenants

Website, Application, Performance DNS & Network
1

What is the name of the domain?

leha.at

What is the issue you’re encountering

Cannot receive mail from other Microsoft 365 tenants

What steps have you taken to resolve the issue?

  • Verified DNS records
  • Verified M365 Settings (Mailflow, etc.)
  • Did testing with several M365 origin domains

What feature, service or problem is this related to?

Mail records

What are the steps to reproduce the issue?

Yesterday we migrated a 350+ staff corporation from Google Workspace to M365.
MX entries have been updated and do now point towards M365.

Emails are coming in fine from many different origin mail servers. However we are unable to receive mail from anybody on other M365 tenants.
Issue looks a lot like this case: Cannot receive emails from Microsoft 365 tenants anymore because of DNS propagation issues

If I got the solution right the issue there was a CNAME at the root level. We do not have any CNAMEs on the root, just a regular A record pointing to an IP.
Any idea what we could do next to trace down the issue?

(Microsoft Support is involved, mail from another M365 tenant to our M365 tenant looks fine on the outbound tenant mail trace, however we are not seeing anything on our side. No problems with mail from non-m365 tenants though.)

Best,
Georg

2

Welcome to the Cloudflare Community. :logodrop:

Your MX record currently contains a hostname that matches the expected format for M365 email.

Unfortunately nothing in the problem you have described involves Cloudflare. The problem exist entirely within th M365 infrastructure. You will need to wait for Microsoft support to assist you.

If you have specific questions about your DNS, we may be able to help you with that.

3

Thanks, epic.network.

It turned out an outdate MTA-STS policy (still pointing to the old MXes) was causing the issue.
Everything good now after we update this.

Might be useful thing to look at for others aswell having a similar issue.

1 Like
4

Thank you for sharing your findings here. It may very well help someone else in a similar situation.

It leaves me wanting to make a feature request for an additional check in the email section of a very useful tool written by Community member @sjr.

https://cf.sjr.org.uk/tools/check

1 Like
5

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