I installed the Transactional Mail Extension and after adjusting a needed Drupal CiviMail permission got it working.
After testing, I deleted the Transactional Mail pseudo mailing, to start fresh, but find that after doing that I get the yellow-screen-of-death and a missing ID error when an event registration or contribution is submitted. I disabled the extension for now-- how do I fix this?
Also, oddly in my tests, each sent email had a duplicate record with an unknown status. Anyone know why? Thanks.