When sending emails to Google mail/Gmail was me getting a bounce email from Google with the following message:
gmail-smtp-in.l.google.com[2a00:1450:4013:c01::1a] said: 550-5.7.1 [2a01:4f8:160:61b3::2 12] Our system has detected that this 550-5.7.1 message is likely unsolicited mail. To reduce the amount of spam sent 550-5.7.1 to Gmail, this message has been blocked. Please visit 550-5.7.1 http://support.google.com/mail/bin/answer.py?hl=en&answer=188131 for 550 5.7.1 more information. u49si23102713eef.172 - gsmtp (in reply to end of DATA command)
The message is very common and the link below, you will find no direct solution. The following helped me:
The message suggested then that the sender mail from an IPV6 address has been sent: 2A01:4F8:160:61B3::2 and that's why I've switched Postfix on IPV4 and voila, It worked:
Change line: inet_protocols = ipv4 and Postfix restart and fetig – No Boune mail from Gmail!