user notification from sme server

I have installed wordpress from the sme server but can’t resolve my email for user notification. I have a separate form, unrelated to wp, set up which automatically sends mail without a problem. However, I am getting an unresolved email issue with this meassage:

Remote host said: 553 #5.1.8 Domain of sender address <[email protected]> does not resolve
and I have no idea where to go to resolve this. I am using anydns to redirect to might site and that works. I have been able to send and recieve mail through horde but this baffles me.