@PStelling There are absolutely no stupid questions! As I’ve mentioned previously, the email world is very complex and nuanced, which is why we’re here to help as much as possible!
When large MBPs like Gmail and Yahoo also start enforcing or making changes, others in the industry tend to follow suit. The requirements Gmail and Yahoo have outlined also apply to all mailbox providers (MBP). They are not new guidelines being implemented and are going from nice-to-have to must-have requirements for optimal deliverability. The end goal for MBPs is to ensure that all incoming mail is authenticated and that the recipient truly wants to receive it.