[scottmotte]

That's a novel thought. I imagine then the native mail apps would expand in settings in order to block some bad senders from abusing that email header.

Tangentially related, iOS mail app has a VIP setting.

[1] https://support.apple.com/lv-lv/HT207213#vip

[buboard]

The apps don’t even need to think of spam, that would be handled by the mail server just like all other spam.