I (mu4e’s author) spend a lot of time dealing with e-mail,
both professionally and privately. Having an efficient e-mail client
is essential. Since none of the existing ones worked the way I wanted,
I thought about creating my own.
Emacs is an integral part of my workflow, so it made a lot of
sense to use it for e-mail as well. And as I had already written an
e-mail search engine (mu), it seemed only logical to use that as a
basis.