email: Changed stray SMTP_SERVER to server

There was a stray SMTP_SERVER left over from config.py from the v2.71 era. Sending by SMTP would error out. 

I greped the code and did not find any more leftovers from that config.py (except for comments).

Commit message:

This fixes the error below that occurred upon sending a message by SMTP.

NameError: global name 'SMTP_SERVER' is not defined.

Signed-off-by: George Saunders <georgesaunders@gmail.com>