I have front-ended my Exchange Server 2010 with sendmail, preferring to use Linux utilities such as SpamAssassin and Clam AV to filter out the bad stuff before sending it to my email server. I also create generic email addresses that I use to give out. Recently, I was having a difficult time sending an email to a newly created email address with a domain that is served by my Exchange Server. In Outlook 2010, after inputting an email address such as special-email@epicminds.com, Outlook would display “this e-mail message cannot be delivered to special-email@epicminds.com because the e-mail address is no longer valid”.

The resolution for this issue cannot be found in Google – no hits are found for the exact error message. It occurred to me that since the Exchange server was responsible for the domain, it was determining the email address was invalid, and this is indeed the case. The solution is simple: change the Type for the Accepted Domain in the Hub Transport from Authoritative to Internal Relay.

To recap:

1. Start Exchange Management Console
2. In the console tree under the Exchange Server select Hub Transport under Organization Configuration
3. Select the Accepted Domains tab
4. Right-click on the accepted domain and select Properties
5. Change the Type to Internal Relay Domain
6. Click Apply

This will enable the Outlook client to accept an email address using that accepted domain that does not have a mailbox tied to the address.