i'm a bit confused as to what Alfresco can do in terms of email notification.
can it only send emails when a user account is registered or can it be set up to send emails when someone checks out a document, changes the version, creates a new document etc?
For checkout and checkin, you can use behaviours but it's also possible to use rules and intercept the creation and the deleting of the working copy. To check whether a document is a working copy, you can read the properties: node.properties["cm:lockOwner"]