[cail]

Technical issues aside, the way AOL implemented poses some issues from SPAM I think.

With AOL I could check and if I can't unsend I know they opened the email. If this worked across all email and I wanted to use email for nefarious purposes I could use this to see, with great accuracy, exactly which email address that I've sent to were active and opened the message. I can then target these accounts more.

I feel like this could be a horrible idea.