reset the mailscanner section in Avast4.ini to default. (See Technical’s avast4.ini section on this board) Setup the mail as if Avast isn’t there and make sure Avast has the apropiate rights in your firewall.
Try to increase both timeouts (of avast into the Advanced tab of Internet Mail provider settings and of your email account, in Properties of the account, Advanced tab too). You can set both to 600, for instance. If you’re on a DSL connection (not dial-up) it shouldn’t be necessary a so long timeout anyway…
Do you use any spam killer? Sometimes the spam killer enters in a ‘loop’ and consume all the timeout. Shutdown it and start it again.
In earlier avast versions mail were routed through the localhost (127.0.0.1) and this would pass through very quickly and/or possibly form a buffer that masked any timeout settings.