Question : Cannot send internal email to certain recipients - Exchange 2010

Hello,

Any help appreciated!

We have an Exchange 2010 setup with no other exchange servers in the organisation. We are unable to send internal mail to the majority of recipients. Users instantly get an NDR with the message :

Your message did not reach some or all of the intended recipients.

      Subject:      test
      Sent:      16/07/2010 11:36

The following recipient(s) cannot be reached:

     First Name Last Name on 16/07/2010 11:36
            550 5.1.1 <[email protected]> User unknown; rejecting

External emails work fine, send and receive. I cannot see any patterns with regards to which accounts this is happening too and which it isn't, but, I can send email from the administrator account fine to internal but not from others.

Mail Flow Troubleshooter does not bring up any errors.

Answer : Cannot send internal email to certain recipients - Exchange 2010

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