Symptoms
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When an email message is sent from a Plesk server to a Gmail account, it fails to be delivered.
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The following error message appears in
/var/log/maillog:ipv6_failed_after_I_sent_the_message./Remote_host_said:_550-5.7.1_[ipv6______16]_Our_system_has_detected_that_this/550-5.7.1_message_does_not_meet_IPv6_sending_guidelines_regarding_PTR_records/550-5.7.1_and_authentication._Please_review/550-5.7.1_https://support.google.com/mail/?p=ipv6_authentication_error_for_more/550_5.7.1_information._hg7si388602wjb.61_-_gsmtp/
plesk postfix/smtp[17181]: connect to gmail-smtp-in.l.google.com[2001:db8:f61:a1ff:0:0:0:80]:25: Network is unreachable
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The sender receives an email with following message:
Remote host said: 550-5.7.1 [2001:db8:f61:a1ff:0:0:0:80 16] Our system has detected that this
550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records
550-5.7.1 and authentication. Please review
550-5.7.1 https://support.google.com/mail/?p=ipv6_authentication_error for more
550 5.7.1 information. la8si618732wjb.94 – gsmtp
Cause
The server has an IPv6 address configured in Tools & Settings > IP Addresses.
Gmail Guidelines for IPv6 are not met: the IPv6 address does not have a PTR record.
Resolution
Solution I: Contact your hosting provider to set up a reverse DNS for IPv6 address.
Solution II: Apply one of the following instructions:
Configure the mail server to use IPv4 only (Postfix)
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Connect to the Plesk server via SSH.
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Find out which protocols are currently enabled with the command:
# postconf inet_protocols
inet_protocols = all -
If the output is the same, modify Postfix configuration file
main.cfby executing the command below:# postconf inet_protocols=ipv4
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Restart Postfix to apply the changes:
# service postfix restart
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Verify the changes:
# postconf inet_protocols
inet_protocols = ipv4
