Feature Request: Rules/Filtering for Outgoing Messages

For reference of anybody who comes across this ticket and has a similar use case: although outgoing rules would still be a nifty feature in MailMate, I actually solved my own use case by using existing functionality in MailMate.

When I originally raised this, I was still getting started with MailMate, and hadn't yet come across the 'message verifications' feature. What I do these days is have an entry in my ~/Library/Application Support/MailMate/Resources/messageVerifications.plist along the lines of:

{
    verifications = (
        {
            title = "Other person not bcc-ed";
            details = "The other person has not been bcc-ed on this message. Are you sure you want to send it?";
            conditions = "(bcc !~[x] 'otherpersonaddress' and from.address ~ 'sharedaliasaddress')";
        }
    );
}

This means if I'm ever sending a message from the shared/alias address, and I haven't bcc-ed the other person, MailMate will prompt me. I can then add the other person as a bcc recipient and re-send the message (and I even have some tricks using Keyboard Maestro to add the bcc entry with a keystroke when necessary).

This completely handles my use case. While it would still be nifty to be able to define an 'outgoing' rule in MailMate so the bcc-ing happens automatically, in some ways you could say that my current solution using message verifications is more flexible, since if I ever want to send a message from the shared address without copying it to the other person, I do have that option.

My use case is that I want people to use a non-exchange address for email. Redirection isn't an option with exchange. So I want to add a Reply-to address to outgoing emails that come from my exchange address. Outgoing rules would fit the bill nicely.

Although I could use David's solution, as far as I can see, that would mean manually the Reply-to address.

@Jon: If I understand correctly then why not just change the “From” address? Do you really want the “From” header to indicate one address and then make a reply go to another address?