Here is a little tip, if you want to do some remote tests yourself, this place has a very good collection of testing tools (lots about email, dns, etc services): http://mxtoolbox.com/NetworkTools.aspx
Based on some "dig" output, I think there is something wrong with your MX records, you have two:
;; ANSWER SECTION:
crdesigns.de. 86400 IN MX 10 mail.crdesigns.de.
crdesigns.de. 86400 IN MX 10 crdesigns.de.
and they point to the same IP address. Just one of the above should be enough.
: My comments are given without warranty, if your dog explodes, tough luck