One of the interesting things that these clients tend to do is deprioritize reading, or marking as read, as the required action of an email. So you can read something a dozen times and it will stick around until you mark it 'complete' (in Mail Pilot's parlance)—and by the same token, once you mark it complete it leaves your inbox and requires a few more steps to revisit. Alternately you can mark something for review—general review, review in a certain topic list, review associated with a certain person, or a certain date.