Make sure the "Contact consents to receive emails" checkbox for the contact is checked.

Hi Scott

Thanks for the reply, yes the consent box is ticked. 

Hi Derick,

1. Make sure the delivery method for Vendors with Multiple Contacts is set to E-mail (Multiple Contacts) under the Processing tab.
2. Make sure you have allocated document types under Multiple Contacts under Vendors.
3. Under Common Services -> Email tab -> tick on Use Email Service.

Hope that helps,

Tim