Waiting for Answer
You have an folder "answer awaited"
When you send out an email there should be an checkbox "answer awaited". This lasts in a copy of the send email into the folder "answer awaited".
If airmail receives new mails where the Subject starts with "Re:" oder "Aw:" etc. - Airmail checks if there is an email with the same subject in den "Answer awaited" folder. If so airmail moves this email to a folder called "answered" ... or something like that.
This would be a really great feature!