Does avast 4.6 home scan thunderbird 1.5rc1 e-mail?
Welcome to the avast forum!
Depends what type of email and what type of operating environment you have.
If you have Windows XP and you have regular POP3 mail accounts then all of those accounts in Thunderbird (whatever version of Thunderbird) are automatically inbound scanned by avast with the Internet Mail provider.
There are exceptions for “non-standard” accounts like Gmail - if you use that we can point you to further help.
So … what operating system are you using and what type of accounts do you have?