email routing to seemingly un-routeable domains

[Jim Pazarena]

I have an issue cropping up with a domain name of:

   sk.sympatico.ca

a user claims that it is a valid domain name for a friend of his, but my
mail server claims it to be un-routeable, and indeed a "dig" doesn't
produce much info.

what happens with names such as these on mail servers which actually _can_
route to it? how do they do it?

Thanks,
Jim