Message recall. Oh dear.
Years ago, I wrote the bulk of this feature. It is not an Exchange feature, but an Outlook feature. It works by sending a custom MAPI message that Outlook recognizes and processes. Of course, this only works if all recipients are using Outlook. It also, after we did some usability testing, only deletes unread email, or email that has not been moved to a subfolder (the original version was quite determined and would hunt down and kill the message even if it had been moved to a subfolder, renamed or entered the email protection program). In this way, it did not violate the UI dictum that the computer move things around when you haven't given it instructions to do so.
So yes, it is Outlook only. If sent to a non-Microsoft mail system, it degrades to a simple notification that the message is being recalled. And it does not a good choice for getting rid of flames you shouldn't have been sending. But within its expected use as a feature - correcting mistakes in email that should have been caught before pressing send, it works fairly well.
But because it is client based, rather than an Exchange feature, it does cause a new mail message to be sent to each original recipient and, combined with a send-all storm, could greatly exacerbate things.
And, preemptively, for those who have philosophical objections to me having written the code in the first place, I'll just have to live with your disapproval and hope my steady paycheck somehow sooths my guilty conscience.
