rails--rails/actionmailer/CHANGELOG.md

* Allow ActionMailer classes to configure their delivery job

    class MyMailer < ApplicationMailer
      self.delivery_job = MyCustomDeliveryJob

      ...
    end

  *Matthew Mongeau*

Please check [5-1-stable](https://github.com/rails/rails/blob/5-1-stable/actionmailer/CHANGELOG.md) for previous changes.