As someone who works in email security I can tell you that it is a never ending cat and mouse game with a lot of false positives as to who is a mouse. Even our customers that have good domain rep, SPF, DKIM, DAMRC, etc still randomly get blocked by filters and large email providers. Part of the problem I see it those large providers and some of the filtering systems send back NDRs that basically provide no information as to why the message was blocked so trying to get your legitimate mail flow working again once someone has flagged you can take days to months as you randomly adjust all the knobs trying to figure out why they are blocking you. I'm sure they would say providing more informant NDRs would make it easier for the spammers to work around the filters. I don't know what the answer is but the current system sucks, it is a huge pita and a dumpster fire for the most part but it's what we have to work with. I'm sure someone will come up with another scheme like DKIM that will become another check box on the list of things you have to set up and once agian few will understand how to implement correctly.