Validate MX records for domains with email?
When this option is set to Yes (as it is by default), the MX records
on virtual servers will email enabled will be validated to ensure that they
point to the Virtualmin system. This is normally what you want, unless you
have a spam filter or other forwarder that accepts mail for your domains
before forwarding it to the Virtualmin system. In this case, you should
select No to prevent false validation errors.