While hunting duplicates, I noticed a leading '-' in some
Message-IDs as a result of RFC4648 encoding. While '-' seems
allowed by RFC5322 and URL-friendly (RFC4648), they are uncommon
and make using Message-IDs as arguments for command-line tools
more difficult. So prefix them with a datestamp to at least
give readers some sense of the age. And shorten the "localhost"
hostname to "z" to save space.