Hello victoria2800,
Thanks for asking the Apple Support Communities for help with an alert about the server identity. Thanks for also providing the screenshot.
The server is trying to access apple.imap.mail.yahoo.com. Possibly some account on your device is trying to access this incorrect server location, which is providing the alert.
You can check in Settings > Passwords & Accounts > Check each account, as the server info can be in any one of them.
If this is your iCloud account, choose iCloud. Scroll down to ADVANCED > tap Mail > check your SMTP servers.
You may need to delete any server showing apple.imap.mail.yachoo.com and enter the correct server address for the Yahoo servers: IMAP server settings for Yahoo Mail
For incoming servers: imap.mail.yahoo.com
For outgoing servers: smtp.mail.yahoo.com
Thanks and have a wonderful day.