Cool, then the next question is what email set-up do you have? At a guess, I would say it was a POP3/SMTP set-up (where you specify and incoming and outgoing server address). If that is the case, then it is likely a server issue with the outgoing or SMTP address. Some ISPs will only allow outgoing server connections for devices currently on their network. If you're request comes in from elsewhere on the Internet, they refuse it.
The solution would be to set-up your email via IMAP or Exchange, depending on what the email provider allows.