This isn’t actually Gmail’s ‘kiss of death’ message. That’s different, and I’ll write another post about that sometime. This is strictly a content issue. The contents of your emails contain words that are instant spam triggers AND Gmail hasn’t seen enough of you.
See, Gmail’s algorithm favors engagement. I could write a whole post about what kinds of engagement, but for now, just imagine replies, clicks, and opens as the important ones. Until it has seen a significant amount of this from YOUR domain, (IP address is irrelevant these days – unless you’re a spammer) you’re probably going to have to be careful at first, and slowly build reputation.
That’s another thing, you have to be super careful NOT to keep mailing when the engagement drops. What I mean is, when you mail say, 2,000 people, and the first 1,000 sends are opening at 12-14%… If you start to see that drop, you’ll want to stop and not let it keep mailing. If you get to the point where you’re seeing 2-3% open rates or lower, you know you’ve triggered their abuse flags. You’ll also want to be careful about speed of sending… but that’s not your issue here, so I digress.