If you need to change or delete a MX (Mail Exchange Record) using the Helm DNS Zone Editor, then please make sure you enter your DNS MX record using the format below.
Record Type: MX (Mail Exchange Record)
Record Name: @
Record Data: mail.yourdomain.com
Record Preference: 30 * MX records only
NOTE: If you need to use an external mail server (non-webecs) then you need to leave your MX record along and simly change the "mail" A record in the DNS Zone Editor to the ip address of the new mail server.