I think that you are getting very close here. When I check the email list on the page you lined to I can see that you have the values set to the id and the label set to the email:
<option value="60">example@site.org</option>
You will need to ensure that you have the email address listed as the value instead of the 60 that you see here. I think you should make the child list use the same email address column for both the label and value.
Also, until you get this working correctly with a single selection type of list you may have problems with the multi select list since it will not post a single value, it will post an array of values to the page. I can give you some pointers on working with the array of values but it is best to get this working with just a regular select list then afterwards update it to be a multi select list.
