A specialized mail gateway system for using user a specified SMTP
server and proxying.

Three proxy modes are supported.
- Unathenticated proxying mode in which case it just sits between
  the client and specified server.
- Athenticated proxying mode, which is the same as above, but only
  for authenticated connection.
- Smart proxying mode in which it accepts will send the mail through
  a server specified in the user's config by matching the the sender
  using regexps to determine what server should be used.