When on, the designated approvers are mailed when a request is created or its approvers are changed, and the requester is mailed when it is approved, rejected or about to expire, and before an active change window closes. The address is the one in each user's Mailer settings; a user without one is skipped. Messages are plain text and carry the request id, the job or scope, the requester, the reason and a link.
This option is shown only while the Mailer plugin is installed.