Removing Watches for a Deleted User
An undeliverable email is sent to a deleted user.
Proper deletion is done by dissociating a user from any can-use permissions. If a user has been removed from the database, their notifications may persist.
Deactivate the user in your Confluence instance. If it doesn't help, you can manually remove notifications from the database by using the following SQL query:
For Confluence prior to release version 5.2.x
DELETE FROM NOTIFICATIONS WHERE username = '<user's name>';
For Confluence 5.2.x and above
DELETE FROM notifications WHERE username IN (SELECT user_key FROM user_mapping WHERE username= '<user's name>');