Bypass comment validation for SOME anonymous users, based on the provided email address? In the case of a low traffic blog (for instance), that only accepts anonymous comments (no user registration) and manually validates them before publishing them, would it be possible to have a sort of internal white list for trusted email addresses (in the comment "email" field)?

The idea would be that comments using one of those addresses would be published immediately, without requiring validation.

(Obviously the email addresses of the commenters are not visible to the visitors.)

Is there a module for that?
Make a rule with event after saving a new comment. Then make a view with the list of emails which should be bypassed. Compare this with the current email of the user, if there is a match publish the comment on the node.
The comparing can be done with views + vbo and the rules action: Load a list of entity objects from a VBO View.combined with a loop statement.