How known?

[Chuck Swiger]

On Dec 1, 2009, at 3:02 PM, Gary Kline wrote:
> hey, mail gurus, how is this possible? thru evolution::
> 
> This is a receipt for the mail you sent to
> <XYZ at msn.com> at 12/1/2009 12:43 PM
> 
> This receipt verifies that the message has been displayed on the
> recipient's computer at 12/1/2009 1:55 PM

Most mail user agents have an option to enable "read receipts"; they use (or abuse) the DSN or MDN capabilities of the recipient's MTA or MUA.  They are not a reliable signal that a human has seen the mail, although they can be used to confirm it at least got to the recipient's mail server or were processed by their MUA.

Knowledgeable mail admins tend to disable them as being needlessly intrusive and wasteful of resources.

Regards,
-- 
-Chuck