Leopard Server Postfix TLS Error: cannot get private key from file /etc/certificates/mycert.key

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.