craigslist does not send warning emails requiring you to verify or update your account.
Scammers often send fake emails trying to steal passwords, or trick users into clicking on fake logins or virus-laden attachments.
Here is an example of a fake "craigslist" email sent by a scammer:
Subject: Important notify about your e-mail account
Hello user of Craigslist.org e-mail server, Your e-mail account will be disabled because of improper using in next three days, if you are still wishing to use it, please, resign your account information. Pay attention on attached file. For security reasons attached file is password protected. The password is "13545".
Cheers, The Craigslist.org team
If you receive a message like this, delete it without following the instructions or opening the attached files.
If your computer is running Microsoft's Windows, make sure your anti-virus systems are up-to-date.