Unable to send an email to Gmail from a Plesk server: Our system has detected that this message does not meet IPv6 sending guidelines regarding PTR records

Kuzma Ivanov

Updated November 20, 2025 07:37

Plesk for Linux kb: technical

Applicable to:

Plesk server has IPv6 address. When an email message is sent from a Plesk server to a Gmail account, it fails to be delivered.
The following error message appears in /var/log/maillog:

CONFIG_TEXT: 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/
The sender receives an email with following message:

CONFIG_TEXT: 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

Gmail Guidelines for IPv6 are not met: the IPv6 address does not have a PTR record.

Solution I: Contact your hosting provider to set up a reverse DNS for IPv6 address.

Solution II: Apply one of the following instructions:

Configure local mail server to use IPv4 only (Postfix)

Log in to Plesk.
Go to Tools & Settings > Mail Server Settings.
Under Outgoing mail mode select Send from the specified IP addresses:
1. for IPv4 - set the desired IPv4 address from the dropdown menu
2. for IPv6 - select None
Apply the changes.

Disable IPv6 addresses on the server

Log in to Plesk.
Go to Tools & Settings > IP Addresses > click on the Sites number next to IPv6. If there are domains hosted on IPv6, go to Domains > example.com > Web Hosting Access and switch these domains to IPv4 only.
When no domains that use IPv6 address in Plesk are left, connect to your Plesk via SSH.
Open the file /etc/sysctl.conf in a text editor. In this example, we are using vi editor:

# vi /etc/sysctl.conf
Add the following lines at the end of the file:

CONFIG_TEXT: net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
Save the changes and close the file.
Apply the changes:

# sysctl -p
In Plesk, go to Tools & Settings > IP Addresses and click Reread IP to update the information about IPv6 addresses.