Tuesday, 16 Jul 2024

SMTP Error 535 Authentication Failed – How to Fix?

As technology continues to evolve, email communication remains a crucial part of our everyday lives. But what do you do when you encounter an authentication failure error while trying to log in to your mail server? This article will delve into the causes of the “SMTP Error 535 Authentication Failed” message and provide you with easy methods to resolve the issue on your own.

Causes for “SMTP Error 535 Authentication Failed” Message

To send messages, your mail client utilizes the Simple Mail Transfer Protocol (SMTP). When the server detects inappropriate authentication, it generates an error message. However, the email program you’re using might display different error messages, or in some cases, no error message at all. Some common reasons for encountering the SMTP error 535 authentication failed message include:

  • Inaccurate Username or Password

If you mistakenly enter the wrong username or password, you may encounter the “SMTP error 535 authentication failed” message. Typically, your email address serves as both your username and password for logging into your mail server. However, certain SMTP servers may require different credentials for added security. In such cases, it’s advisable to reach out to your mail server administrator for further assistance.

  • Disabled Account

Temporary or permanent account disablement can occur due to issues like spamming or outstanding payment dues. A disabled account can also lead to an authentication failed message. Therefore, it is crucial to ensure that your account is active by checking its status. If you encounter any issues, do not hesitate to reach out to your server support team.

  • Connection Encryption

For some servers, you might need to enable connection encryption with SSL/TLS. If you have disabled this option, you may encounter an SMTP error 535 authentication failed message.

  • Authentication Methods

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If your mail server does not support your chosen authentication methods, you may encounter an SMTP error. It is recommended to check the status of your account to resolve any disabled or expired IP-based authentication. While IP-based authentication errors are uncommon, they can still result in an SMTP error 535 authentication failed message.

Methods to Resolve “SMTP Error 535 Authentication Failed” Message

  1. Log in to your control panel and check the current status of your account. Notifications are often provided if your account is facing any issues.

  2. Verify the username and password you provided for logging into your mail server. It is advisable to change your credentials to a more secure one and make a note of them for your future logins.

  3. Block the IP addresses of persistent login attempts to your account. By blocking these addresses at the server’s firewall, you can prevent further unauthorized login attempts.

  4. Enable SMTP authentication on both the server-side and client-side.

    • Enabling SMTP authentication in Plesk:

      • Log in to your Plesk control panel.
      • Go to “Tools & Settings” and select “Mail server Settings.”
      • Select “Relay Options” and choose “Enable SMTP services.”

      If you require assistance, you can contact your Plesk server management service provider.

    • Enabling SMTP authentication in cPanel:
      In WHM, SMTP authentication is disabled by default. Therefore, you need to enable it manually. Follow the steps below:

      • Navigate to WHM and select “Service Configuration.”
      • Choose “Service Manager.”
      • Select the “Antirelayd checkbox.”

      For further assistance, you can reach out to your cPanel server support provider.

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Frequently Asked Questions

Here are some frequently asked questions regarding the “SMTP Error 535 Authentication Failed” message:

  1. What should I do if I forget my username or password?
    If you cannot remember your username or password, reach out to your mail server administrator for assistance in recovering your credentials.

  2. Why is it essential to have a secure password for email accounts?
    A secure password helps protect your email account from unauthorized access, ensuring the privacy and security of your personal and sensitive information.

  3. Can I enable SMTP authentication on any mail server?
    SMTP authentication is supported by most mail servers. However, it’s always a good idea to check with your server provider to confirm if this option is available.

  4. What other factors can cause SMTP errors?
    Apart from inaccurate credentials, issues like network connectivity problems, server configuration errors, or blacklisting can also result in SMTP errors.


In this article, we have explored the causes of the SMTP Error 535 Authentication Failed message and provided you with various methods to resolve the issue. While inaccurate credentials are the most common cause, other factors can contribute to this error. Remember, if you encounter any difficulties, you can seek assistance from server management service providers. Secure your email communication and ensure seamless interaction with the help of these troubleshooting methods.