If you’re encountering authentication errors when trying to send emails from Yandex using Flask, it’s likely due to incorrect configuration of the SMTP server settings or authentication credentials. Here’s how you can troubleshoot and resolve the issue:

1. Verify SMTP Server Settings:

• Make sure you’re using the correct SMTP server address for Yandex. The SMTP server address for Yandex is smtp.yandex.com.
• Ensure that you’re using the correct SMTP port number. For Yandex, the recommended port numbers are 465 for SSL/TLS encryption and 587 for STARTTLS encryption.
• Double-check any other SMTP server settings required by Yandex, such as authentication method and SSL/TLS encryption.

2. Check Authentication Credentials:

• Verify that you’re using the correct Yandex email address and password for authentication.
• Ensure that you’re providing the full email address (including the domain) as the username when authenticating with the SMTP server.

3. Enable Less Secure Apps Access:

• If you’re using your Yandex email account with an application that doesn’t support modern security standards, you may need to enable access for less secure apps in your Yandex account settings. This allows applications like Flask to access your account using username and password authentication.
• Log in to your Yandex account and navigate to the “Security” settings. Look for an option to enable access for less secure apps and make sure it’s turned on.

4. Use TLS Encryption:

• Yandex recommends using TLS encryption for sending emails. If you’re using port 587, ensure that you’re using STARTTLS encryption. If you’re using port 465, make sure you’re using SSL/TLS encryption.

5. Check Firewall and Network Restrictions:

• Ensure that there are no firewall or network restrictions preventing your Flask application from connecting to the Yandex SMTP server on the specified port.
• Test the connection from a different network or device to see if the issue persists.

6. Review Flask Code:

• Double-check your Flask code to ensure that you’re correctly specifying the SMTP server address, port, authentication credentials, and encryption settings.
• Verify that you’re handling exceptions and error responses from the Flask email sending function to identify any specific authentication errors.

By following these steps and ensuring correct configuration of SMTP server settings, authentication credentials, and encryption settings, you should be able to resolve the authentication error when sending emails from Yandex using Flask.