Why is My Gmail SMTP Server Returning a '5.5.1 Authentication Required' Error?

Solve the authentication of the Gmail SMTP server authentication: Security connection requires authentication

When sending emails with the Gmail's SMTP server, the user may encounter an error: "The SMTP server requires a secure connection or the client is not verified by identity. The server response is: 5.5.1 Authentication Required". This error stems from multiple reasons.

Situation 1: The password is invalid

Make sure that the password used to verify the Gmail is correct.

Situation 2: Application login attempt

If you log in to Gmail with your application, please enable less secure applications in the security settings: https://www.php.cn/link/8d060ab1e3879742BD3AF495F407 .

Situation 3: Domain name and IP limit

If the domain name or IP address outside the user's typical time zone is logged in to Gmail, the following steps can alleviate this problem:

Method 1:

View activity, but please note that due to security enhancement functions, its reliability may be limited.

Method 2:

Create remote desktop connection to the production server, and log in from the browser to create an exception to create a server IP address.
• Method 3: Visit https://g.co/allowaccess and click on to enable login from other time areas and IP.
• By solving the fundamental cause of the identity verification error, users can successfully send emails through the Gmail's SMTP server.

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