Your subject says "delivery receipts". Your body say "read receipts".
So WHICH one do you want to discuss? They are NOT the same.
Read receipt *requests* (which is a header in the e-mail) are handled by
the recipient's e-mail client. Whether the e-mail client prompts,
always sends, or always ignores these requests depends on how the user
configured their e-mail client.
Delivery receipt *requests* (which is a header in the e-mail) are
handled by the recipient's mail host (NOT by the recipient's e-mail
client). It is a request for the receiving mail host to notify the
sender that their e-mail got to the recipient's mail service. It does
NOT validate that the e-mail got through that mail service to the
recipient's mailbox and it is does not validate that the recipient
retrieved the e-mail in their e-mail client and then opened that e-mail.
Rare few mail hosts waste their time with positive feedback via delivery
receipts. They don't need to tell you when your e-mail was accepted by
their mail host. Instead they send back negative feedback when their
mail host rejects or otherwise will not or can not accept your e-mail.
The lack of negative feedback is the positive feedback. Mail hosts
don't need to waste their time validating all accepted e-mails and
instead. They just need to provide the negative feedback when they
cannot accept your e-mail (or the sending mail host sends back the
negative feedback when it cannot connect to the receiving mail host).
Read receipts: Requests are handled by recipient's e-mail client.
Most users ignore all such requests.
Delivery receipts: Requests are handled by the receiving mail host.
Most mail hosts ignore such requests.
.
I do get the negative feedback for "failure" so things must be working correctly.
