Here is error report, when it doesn't work:
Nov 4 09:58:08 pmg postfix/smtp[2812391]: B90D347EA8: to=<user@example.com>, relay=none, delay=0.01, delays=0.01/0/0/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=example.com type=AAAA: Host found but no...