Viva.com, one of Europe's largest payment processors, sends verification emails without a Message-ID header — a requirement of RFC 5322 since 2008. Google Workspace rejects them outright. Their support team's response to my detailed bug report: your account has a verified email, so there's no problem.
I’m actually surprised that this post is two hours old and nobody on Lemmy has blamed Google for implementing the required standards or called for OP to host their own mail server themselves on a self hosted European instance.
Jeez, what happened?
Self hosting email is one of the few “you likely shouldn’t self host this” things out there.