How much does GMX email cost?

I'm curious to know, could you elaborate on the costs associated with GMX email? Is it a subscription-based service? If so, what are the various pricing tiers and what features do they offer? Or is it a free service with premium options available? Additionally, are there any hidden costs or additional fees that users should be aware of? Clarifying these details would help me make an informed decision regarding the use of GMX email.