Before you try to debug the email message part of this you need to ensure that you are getting the email addresses into the value of the select list. You should make this a regular select list that has only a single selection first. If you cannot get a select list with the email address as the value this will not work.
I can't trouble shoot this with only the files provided. Do you have a link where I can see your current implementation? After the select list is populated you can view the source on it to see what the values are in this select list. To do any testing on my end I will need a copy of your db in a .sql file.
You will need to first make this a regular select list, then check the source code of the list after adding the email address to ensure that the email address is set for the value.