devise

Mail::Message#delivery_handler

If you assign a delivery handler, mail will call :deliver_mail on the
object you assign to delivery_handler, it will pass itself as the
single argument.

If you define a delivery_handler, then you are responsible for the
following actions in the delivery cycle:

* Appending the mail object to Mail.deliveries as you see fit.
* Checking the mail.perform_deliveries flag to decide if you should
  actually call :deliver! the mail object or not.
* Checking the mail.raise_delivery_errors flag to decide if you
  should raise delivery errors if they occur.
* Actually calling :deliver! (with the bang) on the mail object to
  get it to deliver itself.

A simplest implementation of a delivery_handler would be

  class MyObject

    def initialize
      @mail = Mail.new('To: [email protected]')
      @mail.delivery_handler = self
    end

    attr_accessor :mail

    def deliver_mail(mail)
      yield
    end
  end

Then doing:

  obj = MyObject.new
  obj.mail.deliver

Would cause Mail to call obj.deliver_mail passing itself as a parameter,
which then can just yield and let Mail do its own private do_delivery
method.

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