Robert Chien's Blog

Apple's iChat AV is a very useful application, but sometimes it fails to establish connection with the other end. Most of the time, the failure is due to firewall settings, but on which end? To test, both parties can try connecting to an iChat robot run by Apple; add one of the following test accounts as a new person of Account Type AIM and if the connection establishes successfully, you should see the a video ad.

• appleu3test01
• appleu3test02
• appleu3test03

Below are some commands to capture Mail.app sessions.

In Jaguar the session is recorded in /var/tmp/console.log
In Panther the session is recorded in /Library/Logs/Console/<username>/console.log
In Tiger the session is recorded in /Library/Logs/Console/<username>/console.log

/usr/bin/defaults write com.apple.mail LogActivityOnPort 25
/usr/bin/defaults write com.apple.mail LogActivityOnPort 143
/usr/bin/defaults write com.apple.mail LogActivityOnPort "25,143"

And to disable the logging use this command:

/usr/bin/defaults remove com.apple.mail LogActivityOnPort

Alternately, launch Mail.app in debug mode and send errors to a log file:

/Applications/Mail.app/Contents/MacOS/Mail -LogSocketErrors YES -LogActivityOnHost your.mail.server -LogActivityOnPort 143 &> ~/Desktop/ConnectionLog.txt

Sources http://lists.balius.com/pipermail/mac-users/2005-December/000043.html and
http://developer.apple.com/bugreporter/bugbestpractices.html#Mail

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[UPDATE Nov 21, 2007] More debugging options listed on: http://www.macosxhints.com/article.php?story=2004101603285984