The Mailer plugin allows a site administrator or collection developer to define one or more templates to be used to generate and send email messages out to users, usually containing resource information.
Resource, site, or user information can be automatically inserted into the generated by including special keywords in the email template, as illustrated in the accompanying screenshot. Because an email may include information about more than one resource, the template is broken out into a Body section, which contains the main body for the email, and a List Item section, which is repeated for each resource. The resource list is included in the main body at the point where the X-RESOURCELIST-X keyword appears.
The initial intended use for this was the Rules plugin, to (for example) notify users of new resources or changes in the status of an existing resource, but it can be leveraged by other plugins or custom code for sending email for a wide variety of purposes. Plugins or other custom code can define (and subsequently provide replacements for) their own set of keywords, allowing the set of possible applications for Mailer to be significantly expanded.