This is classic for a tool like that... You know an email isn't sent to some users. You start placing conditional snapshots (like conditional breakpoints but th

This is classic for a tool like that... You know an email isn't sent to some users. You start placing conditional snapshots (like conditional breakpoints but they don't stop) in key locations. You can use conditions like "currentUser == 'user experiencing problem'". Or you can place the snapshots in places where code "should" reach in case of error. Go make coffee. Come back and you'll see stack traces and variable values you can analyze to see the problem. The nice thing is that it will even work if you have a cluster. Just place the snapshot in a tag which applies to all the servers. You don't need to update the code, there's no risk involved etc.