Mail errors · Microsoft 365 and Outlook

What does “5.7.367 Remote server returned not permitted to relay” mean?

A forwarded or relayed message failed SPF or DKIM at the next server.

Last read from the sources at the foot of this page.

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Microsoft Outlook
5.7.367

Remote server returned not permitted to relay

As Microsoft prints it.
01

What does it mean?

When a message is forwarded, the forwarding server becomes the sender, so SPF for your domain no longer matches. DKIM stays valid if the message is not changed.

02

What exactly does the source say?

5.7.367 Remote server returned not permitted to relay This error occurs because of SPF or DKIM authentication failures in forwarded or relayed emails. This problem occurs more frequently in mail flows that include non-Microsoft gateways.

03

Why would a small firm see it?

A forwarding rule, or a filter service placed in front of or behind Microsoft 365.

04

How do I fix it?

  1. Turn on DKIM signing for your domain in Microsoft 365.
  2. Check any service that handles your mail on the way in or out, and set it to keep the message unchanged.
Sources

Where does this come from?

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