Spamassassin is doing it's job here, and doing a good job!

Most spammers and marketing/sales sleezoids never think they are doing anything wrong. They are totally empathy incapable. Or they know they are scum and don't care. Either way.

OP talks about adding "invisible text" and other such common spammer tactics to get around some of the rules. Zero self-awareness.

At no point did this person ever think "did I do something wrong?". No, it's that shitty Spamassassin!