De acordo com o Google
".... you can use Gmail's outbound servers with a different "from" address. If you've already configured the alternate address, your message will be sent from:otheraddress@domain.com, sender:username@gmail.com, regardless of which custom from configuration you chose."
e você pode definir o endereço de no mutt por
The primary way to set your default sender address is through the $from and $realname variables in muttrc:
set realname="Joe User" set from="user@host" set use_from=yes