Both are encryption related. I would guess that GMX has switched (like everyone else did in the last 2 years) to SHA-2.
If that is the case, a firmware update may fix it, it can't hurt to try at least.
We have a Workcentre 7120 and have the scan feature set up to route through a gmx email account. Has been working fine until yesterday when we started getting the message: Completed with an error (027-779) : It attestaion-fail s by SMTP-A. I spoke with Xerox tech support and they told me to confirm the SMTP settings. I logged in and did that but now it is giving a different error: 016-764 : Server Connection error. Nothing has chnaged. Any ideas?