Hello,
I use thunderbird as an email client and with Avast running each email causes my machine to hang for about 1-10 seconds as its is scanned. If I disable Avast everything returns to normal. Is it normal for avast to eat this amount of processing time, the machine in question is a 1.8 Ghz cpu with a gig of ram.
On a slower computer than yours (1Ghz and 512Mb) I have no such problems using Thunderbird 1.5.0.4 with avast Internet Mail scanner set to high sensitivity.
See this thread … see if it helps:
http://forum.avast.com/index.php?topic=20387.0
Also take a look at this Thunderbird extension:
https://addons.mozilla.org/thunderbird/1279/
Hope this helps.