Different from-adresses on same account

[Per-Olof Pettersson]

Hi

I am looking for a feature where you can set the sender of an email.
Eg. I have an IMAP-account where mail arrives at different mailboxes 
(using procmail). Eg [EMAIL PROTECTED] arrives in the folder pgsql and 
[EMAIL PROTECTED] arrives in folder mozilla.

How can I make the sender eg [EMAIL PROTECTED] when sending a message to 
someone?

It seems I can only choose the sender of the message from the dropdown

Best regards
Per-Olof Pettersson