Hello Otmane,
Based on your description the Outlook is sending Delivery and Read Receipt Confirmation for the old emails, my understanding is your Outlook Client may automatically send delivery and read receipts for the incoming emails associated with delivery and read receipts requests, please clarify if I misunderstand your text, thanks.
First please double check if you changed any settings about the email tracking in your Outlook Client. Please click File > Options > Mail > Tracking, then please check if you enabled the Delivery receipt and Read receipt options there, if so, please disable them. And for the option " For any message received that includes a read receipt request: >>> you can select the option " Ask each time whether to send a read receipt". For your reference
Moreover, please double check if you have any emails stuck in the Outbox folder in the Outlook, if so, please back up and delete it from the outbox, after that please empty the Deleted item folder, thanks. And according to the error code you provided above, it is more likely the problem is related to your Outlook Client. If the suggestion above doesn't work, in this case please try the Office online repair and then check if the issue disappears. For more details, please refer to Repair an Office application. By the way, if you have any anti-virus apps in your computer, please temporarily close it and then re-start your Outlook Client to see if it make any difference, thanks.
If the issue persists, I'd like to collect some more information for the further investigation:
1. Before the problem appeared, did you make any changes to your Outlook or email account?
2. Please click File > Office Account and then take a full screenshot about your Outlook Client to me
3. Please take a screenshot about the error message you got in the Outlook when you tried to send emails
4. Where you found the Outlook is sending Delivery and Read Receipt for the old emails? If convenient please provide some generated screenshots about it to me here, thanks.
Best regards,
Oliver
