Prevent smarthost failures from counting towards the defer limit

As a web-hosting provider, I would like to prevent messages that were deferred due to your specified smarthost failing to be counted towards the hourly defer limit for each user.

If, for some reason, a configured smarthost has a small window of maintenance all messages will be deferred, which is to be expected. But these defers might cause a cPanel user to be rate limited because the system itself is not working properly.

Ideally these defers should not be counted towards the rate limit and the mails should stay in the queue until the smarthost is available again and a delivery attempt can be made (which can be deferred due to other arbitrary causes that might indeed be counted towards the rate limit).