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Most of the time, users are seeing this error because of minor typo mistake. Probably, they have entered the incorrect username or TLD domain. So you need to verify that. Also, you need to check the following settings.
1. First of all, you need to Verify that you’ve entered the address with the correct domain (e.g., @yahoo.com, @ymail.com, or @rocketmail.com).
2. Check for typos, such as missing letters, extra spaces, or misplaced dots. Because sometimes, users make the email address with the Dot. So you need to type it correctly.
3. If you’re unsure of the correct email, search your other accounts for messages sent to or from Yahoo.
Once you will make these changes into the yahoo mail account. it will start working fine on your device.