Created attachment 102763 [details] Sample received MS Exchange e-Mail header. KMail doesn't seem to be sending MDNs in response to eMails received from Microsoft Exchange MS-Office365. eMails sent from KMail with a MDN request are responded to correctly -- the MDN is sent. The received e-Mail header is attached but, it's been partially modified to preserve the sender's anonymity. My ISP is 1&1 -- United Internet.
Since 2019, nobody has sent me e-Mail with Microsoft Exchange MS-Office365 requesting a MDN . . . Consider this issue to be closed.