Integrate Alt-Send & Last Mailed
As TSM4 has taken over the mailing UI completely (instead of just a tab)
i would suggest incorporating a feature seen in Postal addon.
Alt-Send - Sends the selected item automatically to currently filled in destination
Auto-Populated last sent name - The To box is automatically filled in with the last user that was sent mail to.
I use the two options together to attach a bunch of loot from my questing character and then alt-click the last item to send the batch, and repeat without typing in any user names because, character 1 will always send to the banker and no one else