On 2026-05-25 13:08, Ralph Seichter via Postfix-users wrote:
* Mel P via Postfix-users:
From my own MX log data, I observe 20-25% of "legitimate" mailhosts
connecting over IPv6. "Legitimate" here meaning those hosts that get
past postscreen's bot countermeasures and DNSBLs.
I wonder if that number might be skewed, to a degree? Servers with both
IPv6 and IPv4 connectivity need not use IPv6 as their first option when
trying to establish an outbound connection.
The true number is probably higher.
Postfix, for example, defaults to protocol balancing without preference.
Without DNS correlation, a dual-stack emitter running postfix is
indistinguishable from an IPv4-only emitter half the time.
Looking at 1-25 May on my primary MX, 868 unique IPs sent 15.3k emails.
Some details of that data:
- 202 (23.4%) were IPv6;
- 536 (61.7%) connected only once, 116 were IPv6;
- 143 had PTRs in google.com, only 1 was IPv4;
- 33 had PTRs in outlook.com, 3 were IPv4;
- 12.8k of those emails came from mx2.freebsd.org, a dual-stack postfix
emitter that connected via IPv6 50.3% of the time;
- 579 of those emails came from GitHub, all from 36 IPs in 192.30.252.0/24.
The observed Microsoft and Google emitters collectively being being
97.7% IPv6 suggests a very significant part of the internet's mail
volume is sent from hosts that prefer IPv6 over IPv4.
IMHO, that last reinforces the idea that it's time to retire the unique
handling of inet_protocols, or at least change it to "inet_protocols = all"
_______________________________________________
Postfix-users mailing list -- [email protected]
To unsubscribe send an email to [email protected]
