Please review these details: Sender: {Sender} Recipient: {Recipient} Check the email addresses, subject line, and date, and ...

Please review these details:

Sender: {Sender}
Recipient: {Recipient}

Check the email addresses, subject line, and date, and search for the message again.

If that doesn't work, contact the sender and ask if they received an email that indicates why the message wasn't delivered (non-delivery report). The problem seems to be happening before the message gets sent. Ask the sender to make sure that the message isn't in their Outbox or Drafts folder.