I'm not a lawyer but I believe it would be very difficult for an FBI prosecutor to raise a case to international status and get a foreign judge to issue a subpoena. Most countries are very protective of spying on their citizens or corporations.

I think the main danger of using a foreign host would be that the NSA has more spying leeway with international traffic so they probably will have already slurped and archived your mail off of the wire without needing to ask your mail host. SSL is supposed to help with that but I have my doubts that that stops the NSA if they want to target you.