Can you make the "@mailbox.org" in the login form implicit?
in the old system I only had to type in my username and password to login. Now I have to enter the @mailbox.org part as well, which I believe should be implicitly assumed unless you enter another address. Gmail has it this way and it feels more fluid.
PS: not sure which category would fit...none of the suggested. shouldn't there be a "UI / UX" category?