What security settings did you change? Did you turn on two-step verification or Account key? If so, then you need to will need to create an 'app password' (you basically have to create separate passwords for specific apps). To learn more, please visit our help page:
This is not recommended and may leave your account more vulnerable to compromise. If you still want to use an app that uses less secure sign in, go to and turn on 'Allow apps that use less secure sign in'. We strongly recommend that you switch to Yahoo's apps such as Yahoo Mail on desktop and mobile and remove your account from all other less secure apps. Location: United States (IP Address: XXXXXXXXXXX) As a result, we prevented a sign in to your Yahoo account ( xxxxxxxx). Older versions of mail and calendar apps such as Outlook). Your account is currently not enabled to sign in from apps, that do not meet modern security standards (ex. This is the message in the response to the attempt:
I changed the security setting as Yahoo advised
