not sure how to block the "secret" notices?
I use swiftpage to send out my broadcast marketing emails.
Tells me who opened the email, who didn't, tells me what links they clicked, how many times, etc., etc. A very resourceful tool in marketing to say the least.
Not sure how it works, but I can tell who just deletes my emails without even opening them and who spends tons of time reviewing them.
www.swiftpage.com fyi