The ideas listed here have already been implemented by GMX.

implemented
Vote
167
points
The GMX Homepage should remember my password Posted by JohntheBaker to Mail-Features, 31 Mar 09 at 11:17
Dear GMX,

a great addition to your service would be a "remember me" function. With it I could check my e-mails several times each day without having to re-enter the information every time.

Thank you very much. [....]
implemented
Vote
114
points
Spell-Checker Posted by lundius to Mail-Features, 31 Mar 09 at 10:19
A spelling correction must definitely be implemented. [....]