Just FYI: SMPT to externals isn't supported, so if you're going outside of x10Hosting and it's working, you're seeing a temporary config error that should soon be fixed. Everything has to go through the outbound spam filter/quantity regulator, has to have a plain text part, and must originate from a valid email address belonging to your hosting account (that is, spoofing the From header isn't allowed). If you're using x10Hosting's SMTP server, you should be okay.