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Ian Chilvers
Asked: 2013-09-19 06:49:20 +0800 CST

Exchange 2010 delivery to postmaster 550 5.1.1 User unknown

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Exchange 2010 has a distribution group setup called postmaster and the Email addresses associated with it are [email protected], [email protected] etc

Internal emails sent to postmaster work fine and go to all members of the group.

However from external via SMTP I get an 550 5.1.1 error saying user unknown.

What have I missed?

All my other Dist Groups work internally and externally, its just this one.

Regards

exchange

1 Answers

  1. Don't usually see the Transport setting for the postmaster email account set to a distro, but ok.

    You're likely getting this from external users because there is still a check requiring the sender to be authenticated (default for distro groups).

    See the pic below...and change the distro group accordingly. Then external senders should be able to email the distro's email address.

    enter image description here

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