I believe this is somewhat out of date. Google did, in my understanding, originally require DKIM and not assign IP reputation to v6 addresses, but that appears to no longer by the case. I turned on v6-outbound on my postfix server and it has had no problems with Gmail (or any other) reachability. Still, many large sites (eg Outlook) only accept mail on v4, presumably for similar reasons, so there isn't much reason to default to prefering IPv6 for outbound mail any time in the next many years.
I suppose the cost of forcing users onto more expensive (by $1/mo...) hosting plans to get IPv4 addresses is not an unreasonable anti-spam measure, but encouraging postfix users to, by default, accept mail over IPv6 would be nice to avoid perpetuating this requirement further. Matt On 7/21/20 2:13 PM, Viktor Dukhovni wrote: > On Tue, Jul 21, 2020 at 02:09:04PM -0400, Wietse Venema wrote: > >>> "By default, Postfix uses IPv4 only, because most systems aren't >>> attached to an IPv6 network." According to Google, third of their >>> users access their service via IPv6. >> >> If 2/3 of all SMTP clients are IPv4-only, then that would be a reason >> not to make this the default for SMTP. > > My server accepts email overs IPv6. Outbound, I don't presently enable > IPv6 by default, largely because operators like Google decided it would > be a good idea to erect higher barriers when receiving email over IPv6. > The result has largely been to slow IPv6 adoption in SMTP, rather than > senders rushing out to jump through all the new hoops. >
