Exchange server cannot connect to remote mail server

I have an exchange 2003 sp2 server that has been running smoothly for a few years now. As of a couple days ago, I am no longer able to send email to one particular domain. I have done a ton of troubleshooting but the result of one of my tests is confusing to me.

All email is stuck in the queue on my server. So I figured I would telnet into the remote server to verify connectivity. I am able to telnet in, but I cannot get a response from the server. When I telnet in, I see the 220 ESMTP...... Here I would normally type ehlo or helo, but when you do that and hit enter, it just hangs there and after a few minues comes back to say the connection to host has been lost.

The even more odd thing is that it is happening on their end as well. They are not able to send my domain any email. This was working smoothly 2 days ago and no changes have been made at either site.

Since I was able to telnet on port 25 I have pretty much ruled out a firewall.

I have ran smtpdiag and all passes except the part where it is trying to connect to the mailserver.

My domain is not using a smart host to send email, but has a front end server to receive email. I believe the remote domain has a front end server to send and receive.

All other email to every other domain is working like a champ.

Any help at all would be great!!!

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SembeeConnect With a Mentor Commented:
Email message flow doesn't just stop for no reason. There will have been a change somewhere in the message path.

It could be a change at your end, at your ISP, at their end, their ISP.

If you have got a message about the user account not existing then that usually means what it says. The SERVER the message was delivered to doesn't recognise the address. What it doesn't mean though is that the message was delivered to the correct server.

Does the recipient have their own email server as the MX records, or is it from an ISP or other host? It could be a change that the hosting company has made and there is no a configuration issue.

ademboAuthor Commented:
I saw this message now appear after trying one more time to issue the helo command:

421 4.0.0 Error: timeout
Either the remote site has a problem with your domain, or they have a problem with their site.
Put both your domain and the remote domain in to
If your domain flags any errors then you need to get them fixed.
If the remote domain fails to accept connections then they have a problem.

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ademboAuthor Commented:
I did try that already and all looked fine. We have been emailing this company for years without issue and they tell me nothing on their end has changed.

I am now able to use smtp diag to successfully run. I notice it takes a lot longer to get a receipt on the destination address I put in. Is there a possibility my connection to them is just timing out? Is that a setting that can be changed?
ademboAuthor Commented:
I must also point out that even though smtp diag is eventually successfully finishing, the email is still held in the queue.
if u cant telnet then u have problem...and it usually is the firewall....who's forewall?? from outside ur domain
do  a telent to both domains....urs and theirs....and the one that fails is the one having firewall problem....
ademboAuthor Commented:

As I stated above: "Since I was able to telnet on port 25 I have pretty much ruled out a firewall."

I finally got a NDR back stating that the email account does not exist at the organizatino the message was sent to. Well I can state with 110% certainty that the email address is indeed good. Also note, it happens on all email addresses at this company, not just the test one I was using.

Thanks for any additional ideas!!!
ademboAuthor Commented:
The remote site had blocked a range of IP's for all traffic, which mine happed to fall in. They fixed that and all is working again.

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