A qpsmtpd timeout error may arise, this is not an issue that is caused by SME server directly, however it can become an issue depending on hardware and configuration settings that are contained in and around other enviroments.
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It is discussed under various names
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*Path MTU Discovery Blackhole http://www.phildev.net/mss/mss-talk.pdf
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*Path MTU Discovery Failures http://www.wand.net.nz/~mluckie/pubs/debugging-pmtud.imc2005.pdf
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*TCP Problems with Path MTU Discovery http://www.ietf.org/rfc/rfc2923.txt
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As discussed in [[Bugzilla:6888]] a workaround was found that may help in mitigating the issue.
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Ensure the MTU setting on your local (gateway) router is set to 1492, then set the MTU on your SME server to 1400 using the following:
