Beyond the records, the things that actually move deliverability, roughly in order:
Reputation of the sending domain and address. Built over time by people opening your mail and not marking it as spam. This is why a brand new domain has a hard first month regardless of configuration.
Separate your streams. Send transactional mail from one subdomain and anything marketing from another. Then a newsletter that collects complaints cannot damage the reputation of your password resets. This is the single most valuable structural decision and almost nobody does it early.
Do not send to addresses that bounce. Repeated hard bounces are read as a sign you are not maintaining your list. Remove them immediately and automatically.
Make unsubscribing trivial for anything non-transactional. People who cannot unsubscribe mark as spam instead, and that is far more damaging.
Content matters less than people think, and it is not zero. Link shorteners, a single large image, mismatched display names and lots of exclamation marks all contribute.
Also check you are not on a blocklist, there are free lookup tools, and check whether your sending service puts you on a shared pool with other senders, since on a small volume you inherit their behaviour.