I have a client running Exchange 2003 on Server 2003 with all updates having the following problem. They are using their local ISP's mail server as a smart host and when someone sends an email to a non-existant or otherwise unreachable domain, the message will clog the SMTP connector queue and/or the unreachable domains queue and begin to multiply in those queues and block unrelated messages from being sent out. The queue information says "The connection was dropped due to an SMTP protocol event sink." When I delete the messages in a queue with an NDR, the recipient gets back a single NDR with only the bad email address, and the backed-up messages then go on their way. This seems to happen most noticably when a message is sent out with a lot of bcc recipients (20-200), but only one may actually have a bad addresse. It also looks like the number of messages stuck in the queue may be the same as the total number of recipients in the message. So basically if they send a message that has even a single unreachable domain in the bcc, the queue fills up with the same number of messages as the number of recipients originally in the message; even though only one address was bad, and all other recipients receive the message. A bit confusing, but any help is appreciated. Thanks, Robert Ramin SouthWest Computer Services

Have you installed GFI Mail Essential on the server before? Please refer the suggestions in this thread for troubleshooting Please run ExBPA against the exchange server for health check James Luo TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Thanks for the reply. I've had GFI Mail Essentials installed for seven years. It's had it's share of bugs in the past but it has been working well since the latest update, which I don't believe corellates to when this issue began, which is within the last 2-3 months. ExBPA didn't find any errors, just some minor informational tips. Robert

Are you sure the email is going through the smart host? This isn't the behaviour I would expect because the DNS lookup (therefore finding the address is invalid) would occur after delivery. I haven't seen an ISP validate the email before it is accepted by their server, as that would be very inefficient. Unless you mean the email is invalid because it isn't correct - so user at example (no .com, spaces, no @ etc). When you have been updating GFI, did you remove the product and reboot, or just in place upgrade? On more than one occasion I have had an update go bad and I have had to remove, reboot and reinstall to get it to work correctly. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Email is definitely going through the smart host, I have confirmed that. The email addresses are invalid because of a bad or non-existent domain name. Messages sent to valid domains but with an invalid or non-existent user do not cause a problem at all. My most recent update for GFI ME was a complete uninstall and reinstall a few months ago. Robert

I would have to point the finger at GFI ME then. Something is doing recipient validation pre-delivery. Exchange doesn't do that. I wasn't aware that GFI does it either, but I haven't looked at GFI ME for a few months. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.