i have the same problem using ipv4
mailcowdockerized-postfix-mailcow-1 | Jan 4 20:27:23 2d162dff7905 postfix/smtp[409]: 1E4659D45E: to=<mail@hotmail.com>, relay=none, delay=265735, delays=265727/0.03/8.8/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=hotmail-com.olc.protection.outlook.com type=A: Host not found, try again)
mailcowdockerized-postfix-mailcow-1 | Jan 4 20:27:23 2d162dff7905 postfix/smtp[413]: 33E889CD48: to=<mail@outlook.it>, relay=none, delay=997, delays=989/0.06/8/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=eur.olc.protection.outlook.com type=A: Host not found, try ag ain)
mlcwuser