SMTP error 535 is a permanent (5xx) error indicating the receiving server rejected your email due to authentication failure. This means your email client or server couldn't provide valid login credentials (username and password) or failed to use the required authentication method. This error can occur in applications like phpmailer and jenkins when sending emails.

What are the cases covered in SMTP Error 535?

Common scenarios triggering SMTP Error 535:

1. Incorrect or Incomplete Credentials: Your email client or server provided wrong or missing login details (username/password) during authentication with the recipient server (phpmailer, jenkins).
2. Failed Authentication Mechanism: The recipient server requires specific methods (e.g., SMTP-AUTH) that were not used or configured incorrectly.
3. Suspended or Restricted Account: Your email account with the recipient server might be suspended, locked, or restricted from sending emails, preventing authentication.

What’s Causing This SMTP Error 535 In Your Servers?

Potential causes of SMTP Error 535:

• Incorrect Credentials: Double-check that the username and password for SMTP authentication are accurate, complete, and belong to a valid sender account (phpmailer, jenkins).
• Incorrect Authentication Configuration: If the recipient server requires specific methods like SMTP-AUTH, configure your email client or server to use them correctly.
• Account Issues: If your email account is suspended, locked, or restricted, contact the email administrator or hosting provider to resolve the situation.

How to Resolve SMTP Error 535 - Step-by-Step Solution

1. Verify Credentials: Ensure the provided username and password are correct, complete, and belong to a valid sender account (phpmailer, jenkins).
2. Configure Authentication: If required, configure your email client or server to use the appropriate authentication methods like SMTP-AUTH.
3. Address Account Issues: If your account is suspended, locked, or restricted, contact the email administrator or hosting provider to resolve the issue.

SMTP Error 535 Examples

• "535 5.7.0 Authentication failed. Please check your username and password."
• "535 5.7.1 Incorrect authentication mechanism. Use SMTP-AUTH for secure login."
• "535 5.5.0 Account locked. Email sending is temporarily restricted."

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