Thanks to Simon Tucker for the list below:
Generally there are 4 things that a domain needs in its DNS Records to be able to send email healthily.
- MX (Mail Exchange) records showing what email service is processing the emails.
- SPF - discloses ip addresses of any servers which are allowed to send email on behalf of the domain.
- DKIM - an authentication key that verifies email is from you
- DMARC - a policy that tell recipients what to do if your email does not have valid entries for the above