Fixup message-id tracking for piped emails
Properly detect and handle empty address lists

The mainly comes in when a MIME header which might contain a list of email
addresses (like Reply-To) is to be parsed, but is empty. The Mail_RFC822
class would return an empty mailbox @ localhost (where 'localhost' is the
default default_domain for mail address list parsing).
Merge pull request #694 from greezybacon/issue/message-id-bugs

Fixup for the message-id tracking feature

Reviewed-By: Peter Rotich <peter@osticket.com>