rails--rails/actionmailer/CHANGELOG.md

• Make ActionMailer::Previews methods class methods. Previously they were instance methods and ActionMailer tries to render a message when they are called.

  Cristian Bica

• Deprecate *_path helpers in email views. When used they generate non-working links and are not the intention of most developers. Instead we recommend to use *_url helper.

  Richard Schneeman

• Raise an exception when attachments are added after mail was called. This is a safeguard to prevent invalid emails.

  Fixes #16163.

  Yves Senn

• Add config.action_mailer.show_previews configuration option.

  This config option can be used to enable the mail preview in environments other than development (such as staging).

  Defaults to true in development and false elsewhere.

  Leonard Garvey

• Allow preview interceptors to be registered through config.action_mailer.preview_interceptors.

  See #15739.

  Yves Senn

Please check 4-1-stable for previous changes.