Great write up. I will almost certainly learn something from it in review. I have run my own company email for around 20 years and other people's for over 30.

Great write up. I will almost certainly learn something from it in review. I have run my own company email for around 20 years and other people's for over 30. I'm in the UK. No matter how technically competent your setup, if your IP is blacklisted by one of the big lists eg Spamhaus then you are screwed. So you need to avoid that. Avoidance tactics involve properly configured MX, A and PTR DNS records. Then you'll need a proper SPF TXT record. Can you do DKIM? DMARC? Oh and please avoid sending spam to people - it ticks them off and get's you blacklisted.