The problem here is that postfix is failing on encrypted TLS certs and OSX ServerAdmin created certs are encrypted. The fix is, as should be expected, to unencrypt the cert:
- cd /etc/certificates
- cp mycert.key mycert.key.saved
- openssl rsa -in mycert.key -out mycert.key.out
- cp -p mycert.key.out mycert.key
- postfix reload
* credit to the apple discussion forums.