Jeff Abrahamson wrote:
> Setting
> inet_protocols = ipv4
> fixes the issue.
I have heard (so apply the rumor filter accordingly) that Google's
Gmail is more strict for IPv6 clients than IPv4 clients. When SPF,
DKIM, DMARC fails then for IPv4 clients it is more likely it will be
accepted and then placed in Junk while for IPv6 clients it is more
likely it will be rejected outright. Or so I have heard.
As a practical matter IPv4 still has good deliverability. So what you
have done by configuring ipv4 is still okay in year 2021 to do. Since
all of the mainstream mail sites still have IPv4 connectivity. As
time goes by this is likely to change as smaller sites become unable
to host IPv4 addresses due to lack of availability.
> I've never seen a DNS query return an ipv6 address, so this behaviour
> surprised me.
Of course this completely depends upon how you have been looking. For
example if one asks only for A records then one will only ever see
IPv4 A records and will never see an IPv6 AAAA record. But Google
definitely publishes IPv6 records. And by default IPv6 will be
preferred if it is available.
Since "dig" and "hosts" have already been mentioned then let me
mention "getent" here. Basically getent uses the same libc lookup as
programs and therefore the same /etc/nsswitch.conf, /etc/gai.conf, and
/etc/hosts configuration too. Whereas dig and hosts are specifically
DNS query tools.
$ getent hosts mx1.smtp.goog
2001:4860:4802:32::97 mx1.smtp.goog
Bob
