I've never mass-sent emails outside of local domain, but I had set up various MTA/MDAs and from I've seen, proper A+MX+PTR records, configured SPF and DKIM, and

I've never mass-sent emails outside of local domain, but I had set up various MTA/MDAs and from I've seen, proper A+MX+PTR records, configured SPF and DKIM, and having proper RFC-compliant emails (and, uh, obviously, not spamming anyone) should be enough to stay way below the threshold.