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We are running Exchange 2003 on our server in a small business environment. We have no known problems receiving email from anyone, with the exception of one client. They send us emails, but their server cannot connect to ours even after many attempts. Sometimes the messages eventually get pushed through, but most of the time we never receive them.

I checked the logs over the weekend and you can see that their server is trying to connect to ours, but then the connection is immediately dropped. This happens every hour for a while, until today at 12:00pm when the connection was made and 3 emails came through. I suspect that they may have manually pushed them through their queue, but I don't know.

Here are some example log entries. These occurred exactly every hour for at least a day and a half (although they may have been more frequent prior to that, because now I am seeing connection attempts every few minutes), with no other log entries from their server:

2012-01-22 16:37:35 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-22 16:37:35 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 16 341 25 16 SMTP - - - -

2012-01-22 17:37:36 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-22 17:37:36 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 16 341 25 0 SMTP - - - -

2012-01-22 18:37:36 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-22 18:37:36 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 16 341 25 16 SMTP - - - -

2012-01-22 19:37:37 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-22 19:37:37 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 15 341 25 15 SMTP - - - -

2012-01-22 20:37:38 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-22 20:37:38 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 15 341 25 0 SMTP - - - -

Here is the log entry from a successful connection attempt from the same sender, from which 3 emails were successfully sent:

2012-01-23 17:59:23 12.34.56.78 - SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 quit. - - 500 0 0 5 5000 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 341 25 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 STARTTLS - - 220 0 0 8 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 STARTTLS - - 220 0 29 8 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 EHLO - +houmf02.sendingserver.com 250 0 339 25 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 MAIL - +FROM:<prvs=362e05761=CRivera@sendingserver.com> 250 0 81 59 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 RCPT - +TO:<recipientname@recipientdomain.com> 250 0 0 42 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 DATA - +<E1BB5FAE0828344A90766FD9D41B9521047EA1BC@houmail02.sendingserver.com> 250 0 191 122457 578 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 MAIL - +FROM:<prvs=362db90fc=TLudwig@sendingserver.com> 250 0 81 61 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 RCPT - +TO:<recipientname@recipientdomain.com> 250 0 0 42 0 SMTP - - - -
2012-01-23 17:59:39 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 RCPT - +TO:<recipient2name@recipientdomain.com> 250 0 0 45 15 SMTP - - - -
2012-01-23 17:59:43 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 DATA - +<E1BB5FAE0828344A90766FD9D41B9521038EBAFF@houmail02.sendingserver.com> 250 0 191 10949737 3250 SMTP - - - -
2012-01-23 17:59:43 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 MAIL - +FROM:<prvs=362e05761=CRivera@sendingserver.com> 250 0 81 59 0 SMTP - - - -
2012-01-23 17:59:43 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 RCPT - +TO:<recipientname@recipientdomain.com> 250 0 0 42 0 SMTP - - - -
2012-01-23 17:59:43 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 DATA - +<HOUMAIL02Mk7LiHdlQg00000511@houmail02.sendingserver.com> 250 0 178 126677 31 SMTP - - - -
2012-01-23 17:59:48 12.34.56.78 houmf02.sendingserver.com SMTPSVC1 RECIPIENTSERVERNAME 10.0.1.10 0 QUIT - houmf02.sendingserver.com 240 8953 94 4 0 SMTP - - - -

Why is this happening, and what can we do to fix the issue so that we can always receive email from this client?

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Using the rule of isolating a single point of failure, it seems like it could be down to the remote server. Have you tried contacting postmaster@sendingserver.com? – Bryan Jan 23 at 22:55
1  
I'm in contact with the admin over at sendingserver.com. For them, we are the only ones who are reporting issues receiving their email. On our end, they are the only ones that we are having trouble receiving email from. – user108032 Jan 25 at 21:24
I did once have a similar problem, but it wasn't just affecting one domain, it was affecting a number of domains, but it was consistently affecting those domains. The problem turned out to be a badly configured DSL router, with an incorrect MTU setting. I don't think this is your problem to be honest, but maybe worth checking, just in case? – Bryan Jan 25 at 21:28
thanks, i'll look into it – user108032 Jan 25 at 22:47
we have an MTU setting of 1500 on our firewall. Should I change that? To what? I read something about 1450 or so. – user108032 Jan 31 at 17:13
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