I have set up exchange to receive email for a secondary domain, for simplicity sake let's say that my primary domain is:
And the secondary domain is: foo.com
Well, in Active Directory Domains and trusts, I set up an alternate UPN suffix for foo.com and then created a user and a mailbox for this, and in exchange I set up a recipient policy to accept mail for foo.com
Earlier today a user reported that an email to @netzero.net was returned as "550 unable to relay for email@example.com" when they used the pop email server "mail.foo.com" however they were able to send the email through thier normal exchange account.
Any ideas on why this occurred?
(i'm happy to clarify further if this isn't enough info...just tell me what you need to know)