Very frustrating problem to track down, and I would appreciate any help/advice anyone here can give me. Exchange 2000, up to date service packs patches, etc. running on a W2K server. Everything is working rather nicely, except for delivery to perhaps 15 domains. Messages go into retry status, event viewer shows that the remote server dropped the connection or failed to respond, logs show an outbound connection attempt and no response. Generally, I can telnet into these boxes and manually deliver a message. I have run SMTPDIAG from the mail server on these domains, and the results fall into one of two categories: SMTPDIAG runs the DNS tests then attempts to connect to the server, and hangs there, or SMTPDIAG successfully connects to the server and everything works fine. I have a couple of domains that get the first result consistently, and others where it hangs sometimes, and other attempts go through without a problem. My knee-jerk reation is "Problem on the receiving end", and that could very well be the problem in all of these cases. Contacting e-mail admins at the affected domains usually brings a response of "we show nothing in our logs from your server, and we receive hundreds of e-mails every day, and you're the only domain that we have a problem with". Well, yeah, there won't be anything in your logs if I can't connect, and I deliver hundreds of e-mails every day without a problem, except to your domain (OK, and a handful of others). The thing that concerns me is that, in general, I can manually telnet into their box and deliver a message, although if it was a general problem with SMTP, I think the problem would be much wider than this handful of domains. I'm not a trained Exchange administrator, I just sort of picked up what I know as I went along, so I would appreciate if a couple of you experts would consider the limited information I have given and offer some guidance as to how to nail this issue down.

Do the messages eventually get delivered? For those that don't, what is the NDR message? And, does it take 2 days for the NDR to be returned (that is the default retry period.) I see all sorts of problems when sending to remote systems. The first thing I do is to turn on SMTP protocol logging on the SMTP first. Give it a few minutes to take effect, then in the Queue Viewer, force a connection. GiveSMTP a minute or two to try the connection and write the information to the protocol logs (c:\winnt\system32\logfiles\ is probablythe location for SMTP log files). That is the first thing. If the connection was established, you should see something indicating why the connection failed. If the connection is never established, that could be other things such as the remote SMTP system rejecting your connection because your PTR record is missing, your SMTP domain is not properly registered in their DNS, or that your IP is on a block list.