There's no shortage of spammers and hackers out there who would love to trick you into giving them your personal information. One way they do this is by sending emails that act as though they came from Yahoo. (See the example below)
Hackers will format emails using logos and verbiage to make you think an email is legitimate. These messages often threaten to close the account or keep you from sending email unless you click on a link. It may also try to "confirm" an account deletion that you "requested". Either way, these emails are fake and didn't come from Yahoo. It's best to delete them right away. The quickest way to tell whether an email came from Yahoo or not is to look for the purple Y logo next to the email in the Inbox.