! This should force all outgoing email (currently at least!) to have a Message-ID. Failure to supply a message id can cause emails to be dropped as spam. sendmail itself attempts to guarantee uniqueness with a hash of microtime, but wherever feasible I've also tried to make the id both meaningful and give it something that should uniquify it. Things like newsletters, though, can't really be uniquified at sending level, so we'll just use microtime to deal with that for us.

Signed-off-by: Peter Spicer <sleeping@myperch.org>