Developer reply by Beonex
Rated 4 out of 5 stars
As long as the authentication with your email server works, everything else works as advertised and very well. But auth can be tricky and sometimes breaks, so I'm deducting one star.
For anyone who has struggled with getting OWL to work with their Outlook.com e-mail: if your Microsoft account has 2FA enabled, you must create an "app password" (via https://account.live.com/) for OWL to use for authentication, rather than using your actual account password. Apparently, OWL does not play well with the 2FA process.
I've already answered you in your previous rating.
FWIW, Owl supports 2FA for Office365 out of the box, without "app passwords".
To create your own collections, you must have a Mozilla Add-ons account.