Admins have been notified and are investigating this further; there looks to be an issue with the system we use to scan for spam prior to the emails being sent.
The mail system has been restarted; it looks to have queued up all emails for about the last 24hr however, so it may take some time to catch up. You may also suddenly get every test email you attempted in quick succession, but that's just proof it's catching up. If it's still having problems after about 24 hours, let us know and we'll go poke the system again.