postfix should be sending emails to @gmail.com addresses now. Turns out it wasn’t SPF, but that the server has no ipv6 routes.
At any rate, we’d want to setup SPF and DKIM records in DNS to guarantee it’ll get through to most Noisebridgers, and its good e-mail hygene.
As @James mentioned elsewhere, Discourse supports reply-by-email and posting-by-email. Configuring these features requires that we add noisebridge.info to the MX record for discuss.noisebridge.info.
I’ve configured postfix to route mails sent to @discuss.noisebridge.info addresses into the mail-receiver container listening on 127.0.0.0:2533 which then sends them here into Discourse.
If someone with DNS access can set up that MX record, then I can work on enabling these features.