How to prevent Drupal to send emails to On hold Contacts in CiviCRM?

[Alan.Guggenheim]

I have now a pretty good list of valid emails in my CiviCRM DB. Several hundred contacts are "On hold" because of typos in their email collected on paper.
But on Drupal, the notifications and subscriptions modules do not know about the On Hold status and keep sending emails to the wrong addresses.
There is apparently no bounce processing in Drupal.
Any idea on how I can prevent Drupal from sending these emails until the email address is corrected and taken out of hold?
Any synchronization between the two?

Thanks