- Start the Mail Protection Wizard (menu Start->Programs->avast! Antivirus), it will launch the mail scanner (ashMaiSv.exe) and schedule its autostart at every logon.
2),3) forget about it, (1) was the cause
After you proceed the wizard, you will probably get an error “port 25 already in use”. Insert this line
SmtpListen=127.0.0.1:26
to avast4.ini under [MailScanner] and change the SMTP port to 26 in your Thunderbird mail account.