Is u_email_update a select box or a list collector?

Populating a List Collector from a script would required using a sys_id.  So in your code you wouldn't use "Update received", you would use a sys_id.  It would look like this:

current.u_email_update = 'sys_id of Update Received';

Your IF Statements for the source make sure those are the correct values for the field.  

Put some logging in there too and make sure you are making it inside your IF statement.

gs.info("INSIDE IF STATEMENT");

Then you can check the script log statements table and make sure you are getting where you need to be.  You can check source values as well if needed by logging those too.

gs.info("The current source " + current.source);