If a client is trying to send e-mail to a domain that has it’s MX record hosted at a external mail server any mail will get stuck internally and will not be sent out. Here is how to fix that issue using cPanel in your VodaHost web hosting account:
Use WHM to edit DNS and change the MX entries and then login to your server as root and do the following
pico /etc/localdomains
remove the domain name
pico /etc/remotedomains