I have Exchange 2007 running with an edge transport server. I am recieving the following error when attempting to send to a newly created distribution list in Exchange 2007 from an external address (such as yahoo):
email@example.com>: host 10.1.1.238[host 10.1.1.238] said: 550 5.1.1 User
unknown (in reply to RCPT TO command)
I can send to this distribution list internally with no problems. I have checked and verified that the "require that all senders are authenticated" checkbox is UNCHECKED.
The IP referenced in the error message refers to our Edge transport server. Anyone able to provide some insight?