Follows the same pattern as controllers and jobs. Exceptions raised in
delivery jobs (enqueued by `#deliver_later`) are also delegated to the
mailer's rescue_from handlers, so you can handle the DeserializationError
raised by delivery jobs:
```ruby
class MyMailer < ApplicationMailer
rescue_from ActiveJob::DeserializationError do
…
end
```
ActiveSupport::Rescuable polish:
* Add the `rescue_with_handler` class method so exceptions may be
handled at the class level without requiring an instance.
* Rationalize `exception.cause` handling. If no handler matches the
exception, fall back to the handler that matches its cause.
* Handle exceptions raised elsewhere. Pass `object: …` to execute
the `rescue_from` handler (e.g. a method call or a block to
instance_exec) against a different object. Defaults to `self`.
When #deliver_now is called all translations within the
generated email will be looked up for the current I18n
locale.
I18n.locale = ‘de’
mail.deliver_now # Generates german email, correct
In #enqueue_delivery the locale was not considered and
the resulting job uses the default locale.
I18n.locale = ‘de’
mail.deliver_later # Generate english email, incorrect
In order to achieve a consistent behaviour the current locale
is now always passed to `ActionMailer::DeliveryJob`.
