There are several steps you can take if you are unable to view or access your sent items in Outlook:

1. Check to ensure you sent the email from the correct account.
2. Make sure that you sent the email to the correct address.
3. Check to make sure the email service is not experiencing an outage.
4. Verify that you have enough storage space in your mailbox and mailbox quota.
5. Review your settings and configurations for Delivery/Read Receipts.
6. Try switching to a different web browser.