Sure, but it introduces an invisible barrier for applicants. Someone who accidentally starts their email that way because they didn't know that hiring managers

Sure, but it introduces an invisible barrier for applicants. Someone who accidentally starts their email that way because they didn't know that hiring managers are doing this kind of filtering accidentally trigger the filter. That's not a problem for the hiring managers, but it adds one more reason why an applicant might get disqualified in a process that is already frustratingly opaque for applicants.