Hi All, not sure why this is not working..
UPDATE 
    ust
SET  
    ust.isUnsubscribedFromSystemEmails = 1
FROM         
    UserSetting AS ust 
INNER JOIN
    [User] ON ust.userID = [User].userID 
AND 
    [User].emailAddress IN (SELECT emailAddress FROM BadEmailAddresses)
In plain English, I am trying to set the isUnsubscribed field to unsubscribed where the userID in the UserSetting table equals the userID in the user table and where the emailAddress in the user table is not in a list of emails from another table. I can run a select on the isUnsubbed column using pretty much the same syntax and it works fine? thanks! 
p.s. I've looked at other similar questions here and the syntax appears the same but obviously I'm missing something.