This only applies to you if you currently have email accounts linked to your domain

Your current hosting company is hosting your website, and email accounts linked to your domain address. Once you update the DNS to ours, or transfer your domain to Apestcontrol, those email addresses will no longer work at the current location. To avoid email problems, those accounts must be created at your new hosting company – Apestcontrol. This is normally a smooth transition, when the email stops working at the current hosting company, Apestcontrol mail servers take over your email accounts.

You should send the list of email accounts you would like to create (via the Helpdesk system) before you update DNS Server Names to avoid any email loses.