Getting Inboxed
You will want to register with several major email providers:
Register with Gmail Postmaster https://www.gmail.com/postmaster/
Register with SNDS https://postmaster.live.com/pm/services.aspx https://sendersupport.olc.protection.outlook.com/snds/JMRP.aspx
Register with ReturnPath https://pages.returnpath.com/get-certified.html
Register with Yahoo https://senders.yahooinc.com/
Use Google's check of MX records: https://toolbox.googleapps.com/apps/checkmx/
Mail.com Postmaster guidelines https://postmaster.mail.com/en/email-policy
https://www.mailhardener.com/tools/
Register with GMX https://postmaster.gmx.net