EHLO or Exchange Server problems? |
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MartinC 
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 Topic: EHLO or Exchange Server problems?Posted: 28 January 2005 at 6:27am |
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We have a problem with one site trying to mail us.
We can mail them, they can mail yahoo but they can't mail us through our external mail servers running Spamfilter. in the logs, the two servers connect but then wait for a minute and timeout with no message sent. I notice their server starts with an EHLO which maybe causing the problem, so we tried setting the EHLO options off in Spamfilter's ini file... this made no difference. we happily receive mail from all other servers (touch wood), so wondered if this was a config problem at the other server's end... perhaps authentication/ EHLO related on their Exchange Server. We also run Exchange but have never seen these problems going to other sites. 01/27/05 00:07:35:016 -- (748) Resolving 193.195.87.117 - evosexch.evos.net 01/27/05 00:07:35:016 -- (748) evos.net is a domain, searching for SPF record 01/27/05 00:07:35:032 -- (748) - SPF analysis for evos.net done: - none 01/27/05 00:07:35:032 -- (748) Mail from: xxx@evos.net 01/27/05 00:07:35:641 -- (748) - MAPS search done... 01/27/05 00:07:35:641 -- (748) RCPT TO: xxx@livjm.ac.uk accepted t 01/27/05 00:08:35:673 -- (748) Disconnect |
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LogSat
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Joined: 25 January 2005 Location: United States Status: Offline Points: 4104 |
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Posted: 28 January 2005 at 10:13pm |
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Martin,
The disconnect most likely happens because SpamFilter has a 60 second timeout where, if not a single
byte of data has been received for 60 seconds, the session is
disconnected.
The good news is that this value
can be changed (by modifying the ReadTimeout value in SpamFilter.ini file), the bad is that there
may be a deeper problem.
We've run into the following
scenario with some users:
The company had an
antivirus/firewall in front of SpamFilter that intercepted emails before they
reached SpamFilter. If a remote user either sent an email with a large
attachment or had a slow connection, the firewall would hold/scan the email for
a long time (> 60 seconds) before passing it onto SpamFilter. SpamFilter
would thus disconnect the firewall before receiving the email. This issue was
easily fixed by increasing the timout value.
Another issue I've seen was with
the Internet Mail Connector in Exchange 5.5. We saw an install of Exchange 5.5
that had a bug in that it would not send the correct end-of-email sequence. All
emails are terminated with the sequence (a dot on a standalone
line):
<CR><LF>.<CR><LF>
in Hex characters this is $0D $0A $2E $0D $0A.
Exchange server would occasionally corrupt that sequence by replacing a 0D
with a 00:
$0D $0A $2E $00 $0A
Since the end of email sequence was incorrect, SpamFilter (and other
applications...) kept on waiting for the correct sequence, which Exchange never
provided, and thus all sorts of problems were occurring. Unfortunately we do not
know if the bug was ever fixed, as Exchange was upgraded to 2000 and the problem
disappeared.
Please let me know if any of these thoughts are of any help. |
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