mjhjmtu

One of the config options in G suite (or google for my domain or whatever its called now) lets one designate some external server to relay outbound email from gmail (i.e. email sent in gmail goes through the external server). I'd like to setup postfix to do this but all the results only cover using postfix to relay to not from gmail.

My understanding is that I would include the gmail ip addresses in my mynetworks setting (or otherwise permit it in smtpd_relay_restrictions). However, the docs for G suite tell us that these ip addresses change frequently and should be dynamically (or at least regularly) inferred via the following procedure:

nslookup -q=TXT _spf.google.com 8.8.8.8

This returns a list of the domains included in Google's SPF record, such as:
_netblocks.google.com, _netblocks2.google.com, _netblocks3.google.com

Now look up the DNS records associated with those domains, one at a time, like so:

nslookup -q=TXT _netblocks.google.com 8.8.8.8

nslookup -q=TXT _netblocks2.google.com 8.8.8.8

nslookup -q=TXT _netblocks3.google.com 8.8.8.8

And I can't figure out how I would automatically set up mynetworks to include this whole list.