Trying to figure out if I need a new domain host, mailhost, or both.

Both are currently US-based "big name" companies, but overseas offices in Asia have frequently recurring problems with sending and receiving e-mail through the domains registered and hosted with them.

Since the offices are in different locales in several different countries, it's hard to ascribe the problem to their respective local ISP's.

Domain host says everything is OK on their end, as does the mail host.

What am I missing?