I have seen some good reviews about the Linux-version, so i have been waiting for the Windows-version.
But, it was a BIG dissapointment !
Here is my quick review of Nylas Mail for Windows:
The installer is uncivilized, it does not ask where to install the program.
Nylas Mail installs in C:\Users\XXXXXX \AppData\Local\NylasMail\, and C:\Users\XXXXXX \AppData\Roaming\NylasMail\.
As most of us know: On a "modern" O/S like fx. W7 the default-folder(s) for installation is C:\Program Files,
and O/S C:\Program Files (x86).
Personally I do not install anything on “C:”, unless i´m forced to by stupid programs (usually created by Microsoft...).
I am using a Linux-style configuration, with multiple O/S, separate partitions for O/S, programs, documents & media etc.
I have a common program-partition for all Windows-O/S, so i install all programs on “E:\Program Files”.
The setup is confusing, fx. if you want to use IMAP for your Gmail-account,
when you have entered the data for the account (email-address, password etc.) Nylas Mail tells you to select Gmail.
Where ???
There is no option on that page to select Gmail....

What they mean is to go back several pages, and select Gmail !?
Then Nylas Mail starts your webbrowser, going to Gmail, requesting that you enter your username and password !?
Why ?
What has webbmail to do with setting up an emailclient !?
I finally managed to get the program installed and working.
But it is very primitive, it looks like "another version of Gmail in a webbrowser", not like an email-client.
And the settings are very limited, although there is an option to use a reading panel, there is no option for where to put it.
It is to the right, which is useless...
There is an option to select different styles for keyboard-shortcuts, but no option to turn it off !?
Very stupid.
Why ?
Because with keyboard shortcuts activated you might accidentally send an unfinished email while you are still editing the text.
Fx. you might have written some 4-letter words, then realizing it would be a bad idea, so you edit the text,
but suddenly the mail is sent before you have removed those 4-letter words.
Ooops...

There is no option to select which folders you want to access and have visible.
Which means that if you have alot of folders it lists all of them....
They call it Nylas Mail 2.0, but considering how confusing it is to install, and the lack of options in settings,
it ought to be called Nylas Mail beta-2.
I uninstalled it after testing.
Nylas doesn´t know how to install programs "properly" (in the right location), neither do they know how to uninstall a program.
The folders where Nylas Mail was installed where still there after uninstalling, so i had to clean up the filesystem manually.
Conclusion: Nylas Mail is no real alternative to FossaMail.
And it will leave garbage in your filesystem after uninstalling it.