The mail proxy Avast installs has problems with gmail on os x 10.6.8, (exerpt from the log):
23.08.2012 20:22:04 proxy[44939] SIGHUP received. Restarting.
23.08.2012 20:22:10 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:10 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:10 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:10 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:11 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:11 proxy[44939] Error connecting to server: connect(): No route to host
23.08.2012 20:22:11 GyazMail[1370] - [GSSL shutdown]: SSL_state() = 0x1220
23.08.2012 20:22:11 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:14 proxy[44939] Error connecting to server: connection timeout
23.08.2012 20:22:30 proxy[44939] Error connecting to server: connect(): No route to host
23.08.2012 20:22:30 GyazMail[1370] - [GSSL shutdown]: SSL_state() = 0x1220
23.08.2012 20:22:30 proxy[44939] Error connecting to server: Connection refused
23.08.2012 20:22:30 proxy[44939] Error connecting to server: Connection refused
This happens in all cases no matter whether eg. the gmail servers have been entered as secure servers or not.