Enable the ability to drag recipients between To/CC/BCC (like in Apple Mail).
When replying to an email originally sent to a group, I often am moving the group back from cc to the to: line (and other clean-up). Very easy in Apple Mail (drag and drop). In Airmail, you either have to copy/paste each recipient or just retype. When you paste, you lose the display name as well (the actual name of the recipient, vs their email address). Kind of a pain.
Jason Sieger commented
Agreed! This function would be really helpful!!
Nikos Korompos commented
This is an absolute must.