The only way to do this would be to edit the default account.

Tools/Accounts select the default account, and edit the details contained therein. You can put whatever you like in the reply address.

This isn't dynamic though, if you want to change the reply address based on the subject or originator of your messages, you'll need to use the "send using" option you mentioned - that's what it's for.

RobAnt

Being a hologram can be a real pain in the assymetric photons! - Vic Fontaine