Personal Filtering
The only thing why I right now not use Airmail is that it is not possible to create personal filters.
What I mean is that I can say:
- when a email is xxx@domain.ltd move to folder / delete / mark unread or read / flag
- when a email has subject xxx move to folder / delete / mark read or unread / flag
So that I can filter my mails faster. The sorting after unread / favorite / flaged / attachment is nice but sorting into folders right now must be done by hand and don't make my life more easy.

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Michael commented
In an ideal world (for me as a GMail user), this would just be an interface for manipulating the server-side filters on GMail.