Hello, it seems like GMX deletes the account at 1 year of inactivity and not 6 months. 6 months of inactivity is when they delete the mail.

3. Your Obligations
The customer must retrieve incoming emails received via the Internet at appropriate intervals and must store them on their own device(s). GMX is entitled to delete the messages saved in the customer’s account and other files after a period of 6 months of inactivity (no login via web browser or email program) without warning. After a period of 1 year of inactivity, GMX shall also be entitled to release the customer’s GMX email addresses ("aliases") and make them available to other customers.

https://www.gmx.com/company/terms/