"An MDN report message has been sent for this message. No more MDN
report should be
sent to the sender."
Not sure what an MDN report message is except it seems to have something
to do with
return receipts which does not apply to any of my sent messages. Thanks
Don't worry about it. The flag is set on all messages you send,
whether or not you have requested the recipient to send a read receipt.
This flag tells Thunderbird that T'bird does not need to ask _you_ to
send a read receipt when you read the message.
This flag is not set on
(a) Messages which will request you to send a MDN (read receipt) but have not yet done so.
This flag is set on
(b) Messages for which you have already sent a MDN (read receipt).
(c) Messages which will never request you to send a MDN (read receipt).
--
Regards
Ralph