Strangely, today an email delivery failed and I decided to investigate further. The email subject was “Mail delivery failed: returning message to sender”
The content in the bounced email was:
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
emailaddress@domain.com
(ultimately generated from xxx@domain.com)
SMTP error from remote mail server after end of data:
host ASPMX.L.GOOGLE.COM [ipv6 address]:
550-5.7.1 [ipv6 address] Our system has detected that this message does
550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and
550-5.7.1 authentication. Please review
550-5.7.1 https://support.google.com/mail/?p=ipv6_authentication_error for more
550 5.7.1 information. z10si11396270par.118 - gsmtp
I’m using VPS hosting with VESTACP and it currently doesn’t support IPV6. However, for some strange reason EXIM (the mail transfer agent) is using IPV4 and also IPV6. I checked this by running the command:
lsof -Pni | grep exim
What I needed to do was disable IPv6 from EXIM so after some research all I had to do was go into etc/exim/exim.conf and add the following line:
disable_ipv6 = true
Save the file and then restart exim by using the following command:
service exim restart
Then check to make sure exim is no longer using IPV6 by using the command:
lsof -Pni | grep eximYou will now see that IPv6 is no longer listed.
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