This article explains how to prevent Outlook from sending a read receipt. Instructions apply to Outlook 2019, 2016, 2013, 2010, 2007, 2003; and Outlook for Microsoft 365.
How to Get a Read Receipt That Confirms Recipient Viewed Email in Outlook [Tutorial]
Some email senders include a request for a read receipt in the messages they send. When these messages appear in your inbox, you may be prompted to send a read receipt confirming that you received and opened the message. If you don't want to respond, set Outlook to ignore these requests. Or, if you want control over how these read receipt requests are handled, set Outlook to respond automatically or to prompt you.
To ensure that Outlook ignores all requests for read receipts:
Go to File > Options.
