Postfix SSL/TLS certificates issue
The option specifies where the root certificates of the trusted issuers are located.

On OS X they are stored in the Keychain.

You can extract them with

$ sudo security find-certificate -a -p /System/Library/Keychains/SystemRootCertificates.keychain &gt; /etc/pki/tls/certs/ca-bundle.crt


And then

smtpd_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt


Edit Keep in mind that when Apple updates the root certificates in the Keychain you will have to export them again.