ENH: ban also submission port (587) for all smtp-related jails

see http://www.rfc-editor.org/rfc/rfc4409.txt
and http://en.wikipedia.org/wiki/Mail_submission_agent

Users of advanced setups might like to split those into multiple jails anyways
to have separate control over submission agents and incoming mail servers.
Merge pull request #277 from yarikoptic/0.9

ENH: ban also submission port (587) for all smtp-related jails