Greetings,
Are you sure the gateway is functioning normally? From your Windows machine, are you able to go to a Command Prompt and successfully ping your ISP's mail server?
Also, regarding the SMTP, if you go to the SME Server Manager and click on email, you can enter a SMTP server that should be used instead of SME's.
Are you sure you haven't made any recent changes to the email settings?
Good luck!
-
Steve