GMX has a hole?

I’m not necessarily talking about a security hole here, but somehow some or my mails simply get lost … The last example was this morning when I asked a friend if he would invite me into Orkut. I waited, waited and … waited. The invitation never reached my mailclient. Then I asked him again to send to one of my other accounts (on other servers) and the mail arrived within a minute. I really start to consider switching from GMX :-? For testing purpose I’m now using GMail as my primary mail service. Let’s see how it works out :-)