Outlook slow to send on 2 PCs, possible slow SMTP response

I have a Linux server running Ubuntu with Qmail as the SMTP server and two PCs in one of the offices will require many attempts to send.  I am told that it sometimes require four hours for a message to finally get out.  I placed a copy of Thunderbird on one of the PCs for testing and messages get out but the progress monitor spins for longer than expected.  Two other PCs in the same office seem to be sending mail to the server without problem.  All 4 PCs are running Outlook 2003.  Other users at other physical locations are not reporting problems.

The two problem PCs have thrown errors when sending mail in the past.  The first time I fixed them by rebuilding the Profiles.  Just recently the same symptoms appeared so I unchecked "My outgoing server requires authentication", closed Outlook, reopened, replaced the check in the authentication check box (found in a web search).  This latter fix was 2 days before the current problem.

I noticed while testing that the telnet command "telnet mail.mydomain.com 25" to this server can take 30-40 seconds before the first response is received but when I try the same using the domain of two other web hosting services the response is instantaneous.  The Ubuntu server is not under a heavy load and web pages are delivered very quickly.

The priority is to get these two problem PCs working but I am not sure if the focus should be on the PCs or if the slow telnet response is the actual cause and these two PCs are just more sensitive to the SMTP delay?  I am looking for ideas on how to diagnose and fix  Thanks.

Tom
ttheimerAsked:
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Mal OsborneAlpha GeekCommented:
First thing I would check is name resolution, if you telnet to the IP address of the mail server do you get an immidiate response?
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ttheimerAuthor Commented:
Telnet to IP address gives the same delay.
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Mal OsborneAlpha GeekCommented:
Ping is immediate? If not, try a tracert, and see where it is slow.
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Daniel McAllisterPresident, IT4SOHO, LLCCommented:
If other systems are sending fine, and only these two systems are having trouble, I'd look at those systems.

In my experience, this type of issue is often caused by either an overly-aggressive (or malfunctioning) AntiVirus, or the presence of spyware that is slowing or blocking the SMTP connection.

I hope this helps!

Dan
IT4SOHO
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ttheimerAuthor Commented:
Ping was not showing a delay.  Using Tracert did not seem to show any delays in reaching the server.  We finally found a recommended solution at http://www.netwerken.it/_knowledge/1767.html that eliminated the delay that we were seeing via telnet.  One of the PCs now appears to be working normally and the other sends all of its mail but throws an error which is probably a secondary issue that will require a profile rebuild.
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