Well I can't come up with a better solution than this cloning way given what was discussed (no wrapper wanted, difficult to change the library itself)
But maybe at least we should put some comments around to say that:

- the Mailer object from the property should not be used directly for calls because it is not reentrant

- we should use the result object from clone_mail instead
It's not ideal to prevent problems but it's better than nothing, and it would clarify the code a bit.

I think we better call this property $mailer in every class

Otherwise, for example later in the EmailResponse class, we end up with confusing parameters
public function __construct($mail, $logger, $email)