Why Am I Getting the '5.5.1 Authentication Required' SMTP Error When Sending Emails?

Email Could Not Be Sent Due to Authentication Issues: "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required"

When encountering the error message "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required" while attempting to send emails through code, the issue may stem from various scenarios:

1. Incorrect Password
Ensure that the password provided for authentication is accurate.

2. Logging In from Third-Party Applications
If attempting to log in using an external application or platform, verify that "less secure apps" have been enabled within Gmail security settings at https://www.google.com/settings/security/lesssecureapps. This will grant authorization for third-party apps to access the account.

3. Attempting to Log In from Different Location/Device/Time Zone
In certain cases, authentication errors may arise due to login attempts originating from a location, device, or time zone that differs from the account's previous login history.

Solutions

For case 1, it is straightforward to resolve by updating with the correct password.

For case 2, enabling "less secure apps" will allow authentication from third-party apps. Alternatively, consider enabling two-factor authentication and generating an application-specific password for use in code authentication.

For case 3, several solutions exist:

• Access the production server remotely via desktop connection. Login from the production server's browser will grant an exception for authentication from other locations.
• If production server access is unavailable, use the link https://g.co/allowaccess to allow login from different locations. This will resolve the authentication issue, allowing you to log in from any device or location.

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