This article applies to Web Hosting and Custom Email accounts only.
There are two ways to do this. The method depends on what you are trying to accomplish.
IF YOU WANT TO REMOVE ALL DOMAINS:
Please open a case with Technical Support team via HostPilot Control Panel > Support (a link in the page header in the top right corner) and explicitly request to remove all domains from the mail server, along with the information that confirms your identity. Removing the domain will result in the immediate and irrevocable destruction of all mail/mailboxes, so be sure that you have gotten all neccessary mail, and that propagation is complete, before you make this request.
IF YOU WANT TO KEEP ANY DOMAINS ON THE MAIL SERVER:
First, make sure that the domain you want to keep is listed as the primary domain on the mail server. If it is not, you will need to switch the primary domain. Once that is complete, the secondary domain(s) can be removed in HostPilot Control Panel > Mail Server > Domains Manager.