How to register a clean domain for your email server?
To Register a New Domain for your Own Self Host Auto Response
Step 1 – Please register a domain name DOTCOM/.org domain from your registrar like Goddy.com, NameCheap.com or Hostgator and etc.
Step 3 – Before purchasing please check whether your domain has any bad history or blacklists. You can do that by entering your domain name here
Only if they are clean from above 4 checking tools, then you can use the domain name for your AR email server.
If you are using your old domain, please do the same check. If any of your domain is in the black list, please go to their link and try to remote your domain from black list.