Ask HN: What's going on with Gmail/O365 email spam filters?

Over the last five years, I've heard and witnessed more and more improper Spam-boxing, and in some cases, complete nondelivery, of initial business intro emails (e.g. after a first meeting, personal referrals, etc).

Prompted by a recent extended back and forth with a colleague who wanted to do some contracting for me, followed up by my email going to her spam box....me having to tell her to find it there...her replying...and having to tell me to find it in MY spam box!

At least one of these accounts is Gmail...the "top" service. What gives? What's better?