They look similar on-screen with the most significant difference being that with Mail.com, you can choose from more than 200 email address domains, such as usa.com, dr.com, catlover.com, coolsite.net, and many others. GMX Mail addresses are either @gmx.com or @gmx.us
How Mail.com and GMX Mail Work
Both services scan every incoming message for viruses, and a learning spam filter keeps the Mail.com and GMX Mail inboxes clean from malware. Flexible filters can sort incoming email into custom folders or forward messages automatically. The web interface for Mail.com and GMX Mail features drag and drop and rich-text formatting. The email providers both support vacation auto-reply, so the service can send out out-of-office emails while you’re away. Messages can be removed from any folder, not just Spam or Trash, after a certain number of days. Mail.com lets you make aliases. You can use them to forward emails sent to those addresses to your main Mail.com email account. This is convenient for protection from spam, and to organize several Mail.com email domains into one account. Both of these email providers include an address book, calendar, and online storage to which you can save attached files.
If You Want Premium Email Service
GMX Mail and Mail.com offer free ad-supported email service. Mail.com also offers a paid premium service that includes the ability to forward emails to another address using the POP3 and IMAP protocols and an ad-free inbox.