I have several different alias's that I use and I want to add a 'from' field when I create a new email message so I can enter a specific alias I want to send from. Is that possible in Mail 3.1?
Mail > Preferences > Composing > "Send new mail from" field.
That just specifies the default "From" address when there are several available, no? I think the OP wants to be able to set it on the fly for each message.
Oh yeah. Uhm. Does the 'reply to' field do that for you? I don't regularly use aliases, but I'm presuming so.
Sort of. But the e-mail would still come from address "A" while replies would go to address "B." Changing the "From" address enables you to keep everything consistent.
Oh, I forgot to mention; There's no 'From' field on 3.1 (apart from in the 'composing' pane)
Sorry...you would list multiple addresses separated by commas in the "E-mail address" field under Preferences --> Accounts --> Account Information. This will give the drop-down menu for "Account" in the message composition window. (Again, this is Tiger...Leopard has to have something very similar.)