Just installed - not used yet - my first impression is that possibly this is better than all email clients I have tested, but...
clicking the new mail icon nothing happens (*)
(a search in your forum did not provide any useful result)
Installed on FF 50.0 on Linux-Zorin
I also had a look at your online documentation - http://www.userlogos.org/docs/simplemail - but nothing found even there...

May you help, Please?
Thank You

* Just discovered that even "reply" button is not operational