Great option you enabled already. Any chance to extend it and (perhaps synch) with the "organisation wide default" addresses we have set up in SF already ? If not, could additional "from" addresses be set up within the tool again?
Background: We think of rolling out the tool to the marketing department too. They however, would need the from address "firstname.lastname@example.org". Changing it in the "setup" of the tool every time will be a pain.
Similarly the option you have now "use Global Sender, Logged In User, Contact Owner" could there be a drop down of addresses defined somewhere else (as mentioned either from the "organisation wide default list" or the manually set up once within the tool).