Action Mailer is framework for designing email-service layers.  These
layers are used to consolidate code for sending out forgotten
passwords, welcoming wishes on signup, invoices for billing, and any
other use case that requires a written notification to either a person
or another system.  Additionally, an Action Mailer class can be used
to process incoming email, such as allowing a weblog to accept new
posts from an email (which could even have been sent from a phone).