Action Mailer MessageDelivery

The +ActionMailer::MessageDelivery+ class is used by ActionMailer::Base when creating a new mailer. MessageDelivery is a wrapper (Delegator subclass) around a lazy created +Mail::Message+. You can get direct access to the +Mail::Message+, deliver the email or schedule the email to be sent through Active Job.

Notifier.welcome(User.first)               # an ActionMailer::MessageDelivery object
Notifier.welcome(User.first).deliver_now   # sends the email
Notifier.welcome(User.first).deliver_later # enqueue email delivery as a job through Active Job
Notifier.welcome(User.first).message       # a Mail::Message object