[corpdrone2021]

We could start doing like the comment on OP does. Send a rejection notice with a link to some list of all the various blogs documenting how big providers refuse to follow the standards.

> My other thought was to have my Postfix server reject all mail from Microsoft servers, with a message requesting the sender to use a different mail provider and pointing to this article.

[southerntofu]

I've often been tempted to do that. However, we would actively be hurting our own users who would be incapable to receive mails from such servers. We'd in fact be hurting the very principles of interoperability we're defending in the first place.

Adding an auto-reply or an email footer mentioning that their providers actively hurts the email ecosystem and linking to alternatives would be a good compromise in my view.

Along with a libre email provider federation, that could go a long way...