Catch specific types of email being sent

[SDB]

Hi

I'd like to know the hook to use, and what variables to check in order to catch the following emails being sent :

- Subscribed thread notifications
I'd like to grab the userid its being sent to, and the threadid and title. Ideally the userid of the user who has replied.

- Private Message Receipt
The user id its being sent to, the userid of the person its from and the subject.

Thanks in advance guys!

Simon