Problem sending to Gmail

jdv

Hello,
I am having a problem with Gmail.
Messages sent to Gmail trigger an error completely at random.
550-5.7.25 [2a01:...] The IP address sending
this message does not 550-5.7.25 have a PTR record setup, or the corresponding forward DNS entry does 550-5.7.25 not match the sending IP.

The problem only occurs on IPv6 and not systematically.

The DNS entries are configured correctly.
Using Google's DIG tool, the PTR of the sending server is correct.

Have you ever encountered this problem?
And how did you solve it?

edumembe

Yes, I’ve seen similar issues with Gmail and IPv6. Even when the PTR appears to be correctly configured and resolves fine with dig, Gmail’s IPv6 checks don’t always seem consistent, especially if the server can send from multiple IPv6 addresses.

In some cases, forcing outbound mail over IPv4 or making sure all possible IPv6 sending addresses have matching PTR and forward records has helped. It doesn’t always look like a clear misconfiguration, but rather how Gmail handles IPv6 validation in certain situations.

Adam

If the reverse PTR is set correctly and you still see the error, make sure the hostname has a matching AAAA pointing back to the same ipv6 IP.

jdv

Perhaps this is because the IPv6 address was not assigned to the server when it was commissioned?

By adding a DNS entry
AAAA mail [ipV6]
to each hostname, the problem appears to be resolved.