laravel/framework — pull request #2860 by anlutro (2013-12-04 21:10:22+00:00)
Title: Ability to retrieve failed message recipients

SwiftMailer's send method accepts a second parameter which is a reference to an array. Failed recipients will be appended to this array. With this small change you can easily do `Mail::getFailedRecipients()` after sending a batch of emails.

https://github.com/swiftmailer/swiftmailer/blob/master/lib/classes/Swift/Mailer.php#L75