On Sat, 2020-11-21 at 13:59 +0100, Thomas Walter via mailop wrote:
> Hello,
> 
> On 21.11.20 12:54, Jaroslaw Rafa via mailop wrote:
> > You can configure your MTA to disable IPv6 only for delivery to Google - at
> > least with Postfix it should be possible.
> 
> how would one do that?

With a custom transport table and a custom master.cf entry.


> We don't know all domains that sue Google MXs, we don't know all MXs
> Google uses and they might change. Do we know Google's IPv6 addresses?
> Do those change?

It's done by destination domain, not IP address.

Here's the relevant transport table entries of domains that I enforce
IPv4 delivery to:

gmail.com               smtp-v4:
google.com              smtp-v4:
googleemail.com         smtp-v4:
hotmail.com             smtp-v4:
live.com                smtp-v4:
outlook.com             smtp-v4:
microsoft.com           smtp-v4:
msn.com                 smtp-v4:
yahoo.com               smtp-v4:
yahoo.com.mx            smtp-v4:
yahoo.co.uk             smtp-v4:
yahoo.es                smtp-v4:
yahoo.com.br            smtp-v4:
yahoo.co.in             smtp-v4:
sbcglobal.net           smtp-v4:
sky.com                 smtp-v4:
rocketmail.com          smtp-v4:
aol.com                 smtp-v4:


Here's the relevant master.cf entry:

# ipv4-only outbound 
smtp-v4  unix  - - y - 200  smtp
        -o inet_protocols=ipv4
        ...


-Jim P.



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