Whenever I send an email to a Gmail address I have this error: Our system has detected that this message does 550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and550-5.7.1 authentication. Please review 550-5.7.1 What to do in the configuration to avoid this problem? Thank you for your help
Add a proper PTR record for your IPv6 address. PTR records are normally maintained in the dns server of the ISP which assigned you the IP address and not on your own server.