Ensure that you’re only sending mail to users who specifically requested it.
Don't send bulk/marketing email from the same IPs you use to send user mail, transactional mail, alerts, etc. Segregate your IPs according to function in order to avoid issues in one type of sending affecting the other.
Authenticate with Domain Keys Identified Mail (DKIM) – This will provide you with a consistent reputation across your domain, regardless of what IPs you send mail from.
Publish an SPF record – this will tell us which hosts can send messages from your domain.
Publish a DMARC record – Messages spoofing your domain will appear unauthenticated and therefore be rejected by us, depending upon your policy disposition.
Provide an obvious and visible unsubscribe process in your mail.
Make it easy for users to unsubscribe from your mailing list.
The unsubscribe process should be easy: overly complicate unsubscribe processes will violate laws such as CAN-SPAM and CASL.