Making one-off changes to the "from" field in OSX Mail

I love Mac OSX Mail, but the one thing that keeps annoying me is that I can't get a free text entry field for the "from" address. I subscribe to different lists using different email addresses within my domain to track spam (i.e. my address for these forums is macforums@mydomain.com and anything not specifically blocked goes into my catch-all) and many lists need a "from" address to match their lists on an automated unsubscribe request.

Is there something which enables a user-editable "from" field from within a single email, rather than having to set up the account in Preferences?

 

Hi - thanks for that. It's certainly quicker than creating a new account each time, just to delete it after I've unsubscribed

However, it only seems to work for POP accounts, not .Mac accounts. I don't use POP accounts - all my domain's email is forwarded to my .Mac account, so I have to set up a non-working POP account for this to work. That'll do for now; but if there were an easier way, particularly a free text-entry field, that would be great...