I am running into an undesired scenario where incoming mail on gmail web interface is properly categorized as spam/phishing, however if the user employs any mail client (ie mail.app, outlook) - the same message categorization is not applied.
Specifically, mail.app and outlook running on macOS 10.14 don’t detect these known bad mails.
In hopes of curbing this, I was hoping to have gmail add custom headers to junk categorized mail, such that I depend on macOS on mail clients level spam detection will trigger and block these messages. I would like Mac mail clients to not leave these messages in the inbox.
I have tried configuring a default routing rule on Gmail to add 'x-gm-spam' and 'x-gm-phishy' headers for downstream mail servers. I still do not see these inserted.
Can someone please let me know if you know a workaround to protect users who dont use the http gmail client from spam?