@Sgarvey You need to pass the contact id in the url, usually I recommend just have a formula field on the object to pull the id.

Then in your button you will need pass the contact field parameter below.

@leighburke yes that worked perfectly thank you so much. Another quick question, can you use the lightening component on the record for email delivery on a custom object?

When i go to send a single email there is no way to add a contact.

Thanks 

Stephen

@Sgarvey  You can use tags on the delivery option to set the contact dynamically, if you need to select from a list of contacts then you would need to use a button.