GMX is a free E-mail provider.
That's the good side.
The company tries to push Pro abonnements to you, sometimes hidden as birthday present, sometimes as anything they can imagine that day.
Even if you're saying no thanks all the times, klicking away those "offers" every week, one day they'll still send you a bill for services never taken.
This is not a single case, it happens quite regularly (do a goodle search!). It's a common practice, sadly not only at GMX.
Well, if you ignore this email or write the support that you've never taken any services (this feedback will be ignored), they send you a second one, signed by an incasso company, raising the costs from about 15€ to 80€. This happens a third time, where you'll finally have to pay around 150€.
Still ignoring/complaining at GMX, they tell you that the process of collecting money is now in the hands of the incasso company, GMX itself is not handling the process anymore. Requesting data with the incasso company, no reply.
In the end, they close your account, for not paid bills, for services you never took.
All your emails and adresses gone.
Of course you never hear from that incasso company again.
Let it be a lecture, choose a free email provider which is not famous for those kind of practices (theres plenty out there!), save yourself time and nerves.
Can not recommend GMX to anyone, advertisement en masse, inapropriate treatment of customers, no support at all. Stay away!