Outlook stores read receipts in the top level of your message store as a hidden message. If you use Send immediately, the receipts are returned immediately, otherwise, the next time you check for new mail, Outlook sends the receipts.
If you don't have access to the SMTP server used by the account when you send/receive, you may receive an error when the receipt attempts to send. If the account exists in your profile, change the SMTP server to a SMTP server you can access and the receipt will be sent.
If you want to delete a receipt, you'll need to use OutlookSpy or MFCMAPI. For instructions on using these applications to delete read receipts, see Delete Stuck Read Receipts using OutlookSpy or Delete a hidden, stuck messages using MFCMAPI
Update: Outlook 2010 stores the read receipts in the data file where the account's outbox is. This is usually the same pst or mailbox where the messages are delivered to, however for IMAP accounts, it's the default data file.
***You may need to configure the Outgoing server tab (look in More Options) to authenticate you with the SMTP server.
***Note Outlook 2000/98 in Internet mail only mode places receipts in the outbox. You can delete these receipts from your outbox.
Published February 12, 2004. Last reviewed on December 27, 2013.