Delivery and Read Receipts

Our organization runs Office 2k (sp3) on XP Pro (sp1)
with an Exchange 2k (sp3) mail server. In general, I've
told people in the past that Delivery/Read receipts are
basically worthless once the message leaves your
organization because there are too many variables in play
with different mail servers and client settings. But
sometimes I get asked for specific reasons why the sender
isn't getting the response they're expecting.

I've researched and read a lot about how delivery and
read receipts are supposed to work, but it is still very
confusing.

If somebody has a link that describes how it works with
different versions of Exchange, Outlook, and other
services like Lotus, Eudora, Yahoo, etc..., it would sure
be handy. I doubt such a beast exists.

The specific question I have has to do with the
reliability of these receipts when going outside our
organization.

Please check my understanding...

In our environment described above, strictly on mail sent
within our organization, Delivery and Read receipts are
sender controlled. The recipient can't avoid sending
these receipts.

When sending mail to an individual who uses Exchange and
Outlook, a delivery receipt should be sent when it
reaches the Exchange server. Whether or not a read
receipt would be sent would depend on if the recipient
has Internet Mail Service Transport installed and what
settings they've chosen for how to respond to read
requests. Is this true no matter what version of Outlook
they're using?

What if, in this scenario, a delivery receipt is not
received, but a read receipt is? Would that mean that
either A) The delivery receipt feature is disabled on the
Exchange server but the read receipt option is turned on
at the Outlook client, or B) the mail server is something
other than Exchange, but the client is Outlook?

Can the delivery receipt be turned off on all Exchange
versions? Will the delivery receipt feature work on non-
Exchange servers? Is there a general rule of thumb that
ISPs follow regarding delivery receipts if they are
providing POP3 mail services?

Thanks for any help you can give. I know I've asked a
lot here.