How to delete an unsent "Read Receipt"

[Guest]

I accidently told Outlook to send a "read receipt" for a
message that was received in an email account that I've
deleted from Outlook.

Outlook is now constantly trying to send the receipt, but
it won't go through since the email account is not in
outlook anymore, so a dialog box is constantly popping up
asking me for proper user id and password.

I don't know how to delete the unsent "read receipt"
message, as I can't see it anywhere.

Thanks much for any help