There are several reasons why this might have occurred:

• The message was never actually sent. Make sure you actually sent the message by checking in your Sent folder. Is it there? If not, you might not have sent it. Do you remember seeing the "Mail Sent" confirmation page that appears after clicking "Send"? It's a page that confirms your email message has been sent successfully.
• The message was saved as a draft. Did you click "Save Draft" by accident? It's the button right next to "Send." Check to see if you saved a draft by clicking your Draft folder.
• The message was not addressed properly. You might have accidentally entered a different email address than the one you intended, or entered a typo that actually turns out to be a real email address. Check to see if this happened by looking in your Sent folder. Take a close look at the address information. Did you write something weird?
• The message was delayed. Most messages are delivered within a few minutes. But messages can sometimes be delayed while in transit due to heavy Internet traffic or routing problems. This kind of delay can last for several hours or more.
• Other possibilities. Occasionally, interruptions or disruptions in email transmissions over the Internet render your message undeliverable. This is very rare, but it does happen. Unfortunately, aside from waiting, there is no way to know for certain whether a message has been delayed or whether it has been rendered undeliverable. The best solution is to re-send your message. You can find it in your Sent folder.