Spam solution

For resolving the problems with sending emails at many users (more 10 users) i propose this solution:

It must block only the users detected as spammers and not all GMX users.
You can implement a system that can you inform that such user is a "spam user" and after a certain numbers of complaints, the account is blocked for sending email during 1 month.

And in foot of emails page's sended by gmx platform it would be to display an link "report spam"