There is the git send-email & co. I understand the extreme convenience of things like github and gitlab but as everything moves onto them it does seem we are becoming really dependent on a few sites.
Have you tried to run your own mail infrastructure in 2023? It's a nightmare from all the junk mail handling schemes of every individual email provider to just dealing with antiquated software for the mailing list and mailer daemons.
I'm not sure why you think you would need to "run your own mail infrastructure" to use git send-email, but you don't.