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i have encountered problem: my users complains that sending process takes too long. The log file show me this:

2015-02-04 15:03:09 SMTP connection from [172.17.20.28] (TCP/IP connection count = 3)
2015-02-04 15:03:09 no host name found for IP address 172.17.20.28
2015-02-04 15:03:43 1YIyfl-0004MR-F4 <= email@example.com H=(localhost.localdomain)  [172.17.20.28] P=esmtpa A=lookup_cram:email@example.com S=2168  id=54D20A7D.2090206@example.com
2015-02-04 15:03:43 SMTP connection from (localhost.localdomain) [172.17.20.28] closed by QUIT

ident timeout is 5s rfc1413_hosts = * rfc1413_query_timeout = 5s

Any ideas?

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  • Probably dns timeout resolving sender or recipient domain (the @something part from their email addresses)
    – Dan
    Feb 4 '15 at 17:01
  • Nope, checked that, but forgot to mention. Equally slow for all domains, even for local ones.
    – Hikaru
    Feb 4 '15 at 17:06
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    In such cases I make a smtp connection by hand (telnet mail.server.name smtp) and simulate sending a mail by hand typing smtp commands (ehlo my.host.name, mail from: <sender@email>, rcpt to: <recipient@email>, data) and see at which one I do not get an instant response. Call me old fashioned.
    – Dan
    Feb 4 '15 at 18:25
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As the commentator has mentioned, from the log message it looks like there is something going on with DNS.

Try doing:

dig example.com

from the command line on the server and see how fast it returns an answer. It should be immediate. If not then work out why dns is not resolving. It is possibke fo mysterious performance issues to be due to the primary DNS failing after a long delay and secondary DNS supplying the answer. You don't get a failure but the primary DNS is always consulted first slowing down the process of getting an answer.

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