Just tested this out on FreeBSD and it works great. So simple!
pki mail.foo.com certificate "/usr/local/etc/mail/mail.foo.com.crt" pki mail.foo.com key "/usr/local/etc/mail/mail.foo.com.key" listen on 1.2.3.4 tls pki mail.foo.com expire 3d # If you edit the file, you have to run "smtpctl update table aliases" table aliases file:/etc/mail/aliases accept from any for domain "foo.com" relay via lmtp://127.0.0.1:2026 accept for local alias <aliases> deliver to mbox # relay out accept for any relay
