there is a unique field validation type included with security assist 2, make sure that security assist 2 is the last extension installed, installing form toolkit or form builder after security assist will remove that validation type.
in the settings for the Unique DataBase value, there is an option to set the key field and key value, on the update page, set this to use the security assist User ID session, this is used to allow the user to re use their email address on update.