I have a customer that would like us to send emails on their behalf using their domain name (@exampledotcom), the emails will need to be SPF, DMARC and DKIM compliant, the issue I am having is that when I add the customers domain to MIAB and the customer has added the DNS details to their hosting platform, I get an error when sending emails to john@exampledotcom but no error if the emails are sending to john@gmaildotcom, the error message I get when sending to john@exampledotcom is that there is no virtual user found on the email server, I am guessing it is because there is no valid user on MIAB, that is because the user john@exampledotcom exists on the customers email server which it should. Obviosuly I have got something set up wrong, if someone could point me in the right direction that would be greatly appreciated.