It looks like you are populating the user defined property incorrectly. The initial string value for the property is just that, a string. You need to use an event to "Set Property Value", and have it set the value for the user defined property. In that way you can create it as a concatenation of both strings and parameter properties. Based on what you have, I think yours should look something like this:
Once created that way, the Email.Send will have the right data to put into the body (make sure you reference the correct user-defined property).