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External contacts do not receive email sent to distribution lists

    Question

  • We have some distribution lists that include external contacts.  Email sent from inside the organization goes through, but email from external does not.  I have checked and the distribution lists are set to receive mail from anyone, no moderation.  It used to work and then suddenly stopped a couple of weeks ago.  

    I have tried changing the external contact in case gmail was blocking it, but the same is true.

    The message trace shows DROP:

    Reason: [{LED=250 2.1.5 RESOLVER.GRP.Expanded; distribution list expanded};{MSG=};{FQDN=};{IP=};{LRT=}]

    But I don't know what that means.

    Any help would be appreciated.

    Monday, July 9, 2018 5:41 PM

All replies

  • If a distribution group has RequireSenderAuthenticationEnabled set to True, then all senders to the group must be mailboxes because only mailbox users are authenticated.  If you want to allow contacts to send to the group, you'll have to set that parameter to $False, but that will allow anyone outside your organization to send to that group.  You might be able to ameliorate that with the use of a transport rule that allows all inside senders and certain outside senders to send to that group.

    Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
    Celebrating 20 years of providing Exchange peer support!

    Monday, July 9, 2018 10:57 PM
    Moderator
  • Hi CTSolutionLLC,

    Agree with Ed.

    You can run the following command to check the "RequireSenderAuthenticationEnabled" parameter:

    Get-DistributionGroup DLName |fl Name,RequireSenderAuthenticationEnabled

    If the value is not false, try to change it to false via the following command and check again:

    Set-DistributionGroup DLName -RequireSenderAuthenticationEnabled $false

     

    Best Regards,
    Niko Cheng


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    Tuesday, July 10, 2018 7:34 AM
    Moderator
  • Hi ,

    I'm just writing to check how's everything going? If you have any questions or needed further help on this issue, please feel free to post back. If the issue has been resolved, please mark the helpful replies as answers, this will make answer searching in the forum easier and be beneficial to other community members as well. Thanks for your understanding.


    Best Regards,
    Niko Cheng


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.


    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Monday, July 16, 2018 9:45 AM
    Moderator