Ok, sounds like I did understand that. So, as I mentioned, the issue is with this data string - "ST/BL/CV/EL". There is no easy way in InfoPath to match that to the values like "CV", "EL" and so on in your email list. However, if they are unique, we could maybe use contains. I'm worried about a false positive with contains, like if you had a group named "ST" and another named "BST" or something. At any rate, I've attached a simple sample - pick a value from the second dropdown and the field below should show the emails.
Hilary Stoupa