I am not sure a mailing list would be the best solution here. If any GitHub activity is posted there, it would become impossible to follow really quickly. Maybe a bot, which sends an email to the bpo-email of the original bpo-committer is a better approach.
Just to make sure everyone understands correctly. What I am saying here is that when a person with no GitHub access proposes a patch on the bpo, then the bot which converts the patch to a PR registers the contributors registered bpo-email to another bot(let’s call it the “mail(wo)man”), which then sends GitHub-like notifications to the contributor for every GitHub update.
I don’t really know, if that’s possible, but I think it is a more reasonable idea than a universal mailing list. Any thoughts?