First, check with the sender to make sure that the message was actually sent and that the sender isn't having mail server problems. If that's not the problem, one of the following may have occurred:

The message arrived for you after you signed in. You may wish to check periodically for messages received after you sign in by clicking the Inbox link.

The message was not addressed properly. The sender may not have your correct email address or may have accidentally entered an incorrect email address. If the incorrect address entered happens to be a valid address, someone else may have received the message intended for you. If the address entered was invalid, the message should have been returned to the sender with an error message.

The message was delayed. Most messages are delivered within a few minutes, but messages can sometimes be delayed in transit due to problems on the sender's mail server, heavy Internet traffic, or routing problems. (On rare occasions, delays can last for several hours or more.)

The sender's address is blocked. The Blocked Email Addresses feature in the newest version of Yahoo! Mail allows you to create a list of addresses from which you don't want to receive mail. Mail coming in from one of these senders will neither arrive nor bounce; it will simply be deleted. Learn how to check your blocked addresses.

You've enabled mail forwarding. If email is being forwarded to another email address, it will not be received in the Inbox. Check if your mail is set to forward to another email address.

Other disruptions. Occasionally, interruptions or disruptions in email transmissions over the Internet will render a message undeliverable. While this is very rare, it does happen. Unfortunately, aside from waiting, there's no way to know for certain whether a message has been delayed or whether it has been rendered undeliverable.