https://github.com/search?q=repo%3Ametabrainz%2Fmusicbrainz-server%20message_id&type=code

The message ID isn't guaranteed to be unique because it uses `time()` with second precision, and if multiple accounts are created within a second they end with same message ID.

See https://github.com/metabrainz/musicbrainz-server/blob/c81fa1c2a359d46381daf2cbdb57ae422d97213c/lib/MusicBrainz/Server/Email.pm#L98