bettati,
This might not be that helpful, but I, too, am using 6.0.1 with both ClamAV and SpamAssassin installed and am experiencing timeouts when trying to send mail. Some of my staff are still using Outlook Express, but many have already been migrated over to Thunderbird. This affects both LAN and WAN users, though does not appear to be a problem using WebMail. It appears that the email is, in fact, being sent however the problem lies in copying the email to the sent-mail folder. This seems to be where the timeout is happening.
Unfortunately, because this is a production server, we are not in a position to disable ClamAV and run for a period for testing whether or not this has any impact on things.
My problem started after having the server crash with the "Drive exceeded Failure Prediction Threshold" error message which forced me to rudely reboot the server. Since then, I've been monitoring the 4 SCSI drives in the box and have found that one of them runs 13 degrees hotter than the other 3. I have not found an explanation for this yet.
Is anyone else having troubles such as this?