In a company I worked for 20+ years ago the IT set up an email "spam filter" that used a big list of regexes, but the problem was the filter ran on the raw mess

In a company I worked for 20+ years ago the IT set up an email "spam filter" that used a big list of regexes, but the problem was the filter ran on the raw message, so it also filtered SMTP headers. I noticed this when an email that was routed through smtp123.essex.hp.com or something similar never arrived to my mailbox.