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Email To/From Microsoft Distribution Lists failing

My organization uses Microsoft 365 with Sophos Central Email Security as the email filter.  The DLs contain both internal and external email addresses, such as Gmail or Yahoo. When I send email from an internal address to the DL, everything gets delivered.  When an external address sends to the DL, the internal addresses receive but the external addresses fail.

I cannot see any error messages from within Sophos.  The external reject message is


550 5.7.1 XGEMAIL_0011 Command rejected

Message rejected by:

This is a problem for my organization.  Any tips/help?

Added TAGs
[edited by: Raphael Alganes at 12:57 PM (GMT -7) on 17 May 2024]