Is it possible to capture every mail sent from a domain with a script?

Not sure that make sense but basically my problem is, my site is a combination of integrated scripts. about 3 or 4 different scripts. Each one has a different method of sending mails. my host has a cap on mail (100 per hour) which most host have anyway. now when user's send mails to other members or when an update occurs which prompts a notification that a user subcribes to. An email is then sent alerting them. now if i'm over my usr quota then obviously mails dont get sent.... what i'm looking for is a way to collect every mail sent from all the scripts and pass details on to a script for mysql storage after which i'll write a script to send some of the emails every hour. the current problem is that some mails wont get sent and i want to sort that out, even if it takes up to an hour or more for notifications to be sent, at least they will be instead of users not being notified at all.

Is there any way to get any attempt of using sendmail or postfix from my domain before the mails are sent? any clues or pointer in da right direction are welcomed and will be greatly appreciated. thanks in advance.