PA Bear [MS MVP] wrote:

It works best and most reliabily when the Sender is also using OE.
YMMV if Sender's using another Mail Client.

Why? The "read receipt request" is just a header that gets added to the
e-mail. The e-mail client doesn't define the structure or value of the
headers. RFCs do.

One of the following headers are in the received copy of the e-mail (see
http://www.ninebynine.org/IETF/Messa...g-mail-00.html
for short descriptions):

Read-Receipt-To
Return-Receipt-To
Return-Receipt-Requested

Disposition-Notification-To
Generate-Delivery-Report

Some are obsolete or invalid/non-standard (but Microsoft used them at
some point, anyway). Only the last 2 are standard and inserted into the
sender's message headers. Disposition-Notification-To is the read
receipt request that the recipient's e-mail client must answer.
Generate-Delivery-Report is asking the receiving mail server to send
back a status e-mail; however, most mail servers ignore this delivery
notification request since the lack of negative feedback via a
non-delivery report (NDR) e-mail equates to a positive report, and mail
servers are more interested in identifying what they can't deliver
rather than identifying the much larger number of all messages they will
accept. Both these headers have as their value the e-mail address to
which the confirmation e-mail gets sent.