Fro time to time we are experiencing many "The smtp session has timed out." errors that lead to duplicated mail to the destinations.
It seems that at some point during the comunication with destination SMTP servers the delivery process freezes just after the message is delivered but before there's an "OK" from the destination.
This results in this issue: SM think that the comunication is broken and after 60s it will close the cominication with TimeOut adn retry again later, but the destinations has received the massage. So the message will be resente many times and there's diplicates in the destination mail directory.
Changing the timeout to 180s does not solve teh issue.
SmarterMail is the latest 15. version in a dedicated Windows 2012 R2 STD Server.