I'm using Laravel 4.2, IronMQ and Mailgun to send emails on the live site. For some reason two - sometimes three - copies of the email are being sent, about two minutes apart.

Mail::queue(
	$templates,
	$template_data,
	function($message) use ($template, $parameters, $recipient) {

		// Address the message.
		$message->to( $recipient )
		        ->subject( $parameters['subject'] );

		// Add any additional recipients.
		if ( isset($parameters['reply-to']) )
		{
			$message->replyTo( $parameters['reply-to'] );
		}
		if ( isset($parameters['cc']) )
		{
			$message->cc( $parameters['cc'] );
		}
		if ( isset($parameters['bcc']) )
		{
			$message->bcc( $parameters['bcc'] );
		}

		// Add any attachments to the email.
		if ( isset($parameters['attach']) )
		{
			if ( is_array($parameters['attach']) )
			{
				foreach ($parameters['attach'] as $file)
				{
					$message->attach( $file );
				}
			}
			else
			{
				$message->attach( $parameters['attach'] );
			}
		}

	});

In my development environment I use sync for queuing, which doesn't appear to have the same issue.

My question is: how can I prevent the emails being sent more than once?