It's probably something in the potential spam filters that bots have either attempted to use that domain in the past. Use a GMail, Outlook, or something very common.
I would think that's not it, but so as to give the benefit of the doubt, I just successfully registered one with a hyphenated domain, so that's not it.
That might be best dealt with by customer support. I would not make mention of whether it is "foreign" or not, that might cause confusion. An email address is an email address...
