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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 <> 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.

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up vote 2 down vote accepted

Have you used the message tracker to confirm that the message is indeed somewhere in your system?

And do you have a catch all script, maybe that's the mailbox to check?

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I found the message in the Message Tracker, and it appears to track normal delivery. The last entry is "SMTP Store Driver: Message Delivered Locally to Store <my email>". Checking my mailbox more thoroughly turned the messages up in a subfolder of Inbox, where a rule has been delivering them. So it appears to be working now. But I've had it not deliver messages before; if it happens again I'm coming back to this question. Thanks anyway. – Mr. Jefferson Feb 23 '11 at 17:29

"Queued mail for delivery" means that the server accepted the email. Do you have the IMF installed and enabled? If so, it may be dropping the message. Are there any third party spam filters in use on the server or client?

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There is no filtering going on at the client level; it doesn't arrive in the web mail, my iPhone or Outlook. Intelligent Message Filtering appears to be installed; its tab is available under Properties of Message Delivery, but it's not visible under SMTP under Protocols. In the tab under Message Delivery it's set to archive messages that it "blocks", but my messages are not in the archive folder. – Mr. Jefferson Feb 23 '11 at 17:15

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