Replacement for default mail handler that queues mail sending. This includes emails sent from anywhere within the site (private messages, activity notifications, etc).

All queued emails will be sent every five minutes, and once sent they will be deleted.

You need to set up cron on the server to trigger the "fiveminute" cron plugin hook.

Based on Message queue plugin by Kevin Jardine (http://community.elgg.org/pg/plugins/project/515768/developer/kevin/message-queue)