GMX Mail has a stupid quirk about logging you out after only a few minutes. They claim that this is done for "security" purposes, but with today's anti-virus softwares and firewalls this is no longer necessary.
After logging back in, you are greeted with an obnoxious message that basically says: "You logged out incorrectly" when you didn't log out at all. This is most inconvenient, and it happened once when I was merely selecting multiple addresses from my contact list. How stupid can these people be?