How do I remove previous requests of "receipt of email" in Outlook 2007?

Right now I am traveling overseas and am using my same email address to receive, but a different internet provider to send emails. One friend's email always ask for "a receipt" that this email has been received. I inadvertently said yes to about 6 emails at different times. Now when I am in Outlook 2007 and click "send/receive," it automatically is trying to "send" these receipts, although there is no "email" in my Outbox. How can I "purge" or remove these previous requests, so that Outlook is not trying to send these?