Election Notifications on mailing list are not delivered to GMX mail-accounts

Summary

For a while notifications about elections (commiter/project-lead) which are send to dev-mailings upon creation are not delivered to my Email inbox. I noticed that multiple times already for M2E and PDE and even completely missed one election because of that (in other cases I noticed them in other ways). My mail-account is from GMX Mail. I also checked my Spam-folder but the mails weren't there as well. Others with different E-Mail providers/hoster probably don't have the same issue.

Do you have any hints how that can be solved? Could it be that the notifications are already blocked at the GMX-servers before they reach my inbox?