For a variety of reasons, I am needing to programmatically send mail through an Exchange 2003 server. I'm not able to use any built-in "SmtpClient" classes so I'm following the SMTP protocol over telnet in order to do it. It worked at one time, and then the server stopped delivering mail to internal addresses, though mail sent to external addresses continues to work. I always get the response
250 2.6.0 <abcabckRojQiikgkrYg0000000b@mail.mycompany.com> Queued mail for delivery but the mail never arrives, and I can't find it in any junk/bad mail folder or any queue either in my account or on the Exchange server. If I telnet manually into the server and do it all by hand, I can send some mail, but mail that looks like what is sent programmatically does not get sent.
Is there some kind of filter on Exchange Server that blocks mail sent in this manner after a while? Or some junk mail level that never even gets to the user's Junk Mail folder? I already looked at the Relay settings, and the computer running this program is in a subnet that is Allowed in the relay list.
UPDATE: the messages turned up in a subfolder of my Inbox, where a rule has been moving them. So it's currently working. But I've had it not deliver messages in the past, and they weren't going to that folder either. If I catch it again, I'll come back and note it here.