Unfortunately, does not work with third party cookies disabled.
I am really terribly sorry for any trouble this has caused.
DarwinMail currently uses a cookie for your email address once you have authenticated with it.
I am however in the process of removing this cookie and using local storage instead :)
If you have any issues enabling third party cookies, I have created a guide for every major browser in the FAQ section of our homepage :)
It's good that you're getting rid of that dependency. It's usually only few crummy web shops and flight/hotel booking that have issues working without a secondary insecure browser.