18 Send Smtp Mail Message 535 5.7 3 Authentication Unsuccessful Solutions

Hello everyone, I’m Kent, the website admin. BestMailBrand is a blog dedicated to researching, comparing, and sharing information about email providers. Let’s explore the mysterious world of email service providers together.

When trying to send SMTP mail messages, encountering the error "535 5.7.3 Authentication Unsuccessful" can be frustrating. This error indicates that the SMTP server has rejected your authentication attempt. Fortunately, there are several potential solutions to this problem. In this article, we'll explore 18 different solutions that may help you resolve this issue.

Solution 1: Check Your Credentials

The first and foremost step is to ensure that you are using the correct username and password for SMTP authentication. Double-check your credentials and make sure there are no typos or mistakes.

Solution 2: Enable Less Secure Apps

If you're using a Gmail account, you might need to enable "Less Secure App Access" in your Google Account settings. This allows apps that use less secure sign-in technology to access your account.

Solution 3: Use App-Specific Passwords

For accounts that support it, such as Gmail, you can generate an app-specific password to use for SMTP authentication instead of your regular password.

Solution 4: Update Your Email Client or Library

Make sure your email client or the library you're using to send emails is up to date. Outdated software might not support the latest authentication methods.

Solution 5: Check Your SMTP Settings

Verify that your SMTP settings, including the server address, port number, and encryption method, are correct. Mismatched settings can cause authentication failures.

Solution 6: Check Your Firewall or Security Settings

Ensure that your firewall or security software is not blocking the SMTP connection. You might need to add an exception for your email client or the SMTP server.

Solution 7: Contact Your Email Provider

If none of the above solutions work, contact your email provider for assistance. They might have additional insights or specific instructions for their service.

Solution 8: Two-Factor Authentication

If you have two-factor authentication enabled on your email account, you might need to generate a special password for use with SMTP.

Solution 9: Check for Server Outages or Maintenance

Sometimes, the SMTP server might be down for maintenance or experiencing outages. Check the status of your email provider's servers.

AOTsend is a Managed Email Service API for transactional email delivery. 99% Delivery, 98% Inbox Rate.
Start for Free. Get Your Free Quotas. Pay As You Go. $0.28 per 1000 Emails.

You might be interested in:
Why did we start the AOTsend project, Brand Story?
What is a Managed Email API, How it Works?
Best 24+ Email Marketing Service (Price, Pros&Cons Comparison)
Best 25+ Email Marketing Platforms (Authority,Keywords&Traffic Comparison)

Solution 10: Review Your Code

If you're sending emails programmatically, review your code for any potential issues that might be causing authentication failures.

Solution 11: Use the Correct Authentication Method

Ensure that you're using the correct authentication method supported by your SMTP server, such as PLAIN, LOGIN, or CRAM-MD5.

Solution 12: Disable Any VPN or Proxy

Sometimes, VPNs or proxies can interfere with SMTP connections. Try disabling them and see if it resolves the issue.

Solution 13: Clear Cached Credentials

If your email client or operating system is caching old credentials, clearing them and re-entering the correct ones might help.

Solution 14: Update Your Operating System

Make sure your operating system is up to date, as outdated systems might not support the latest security protocols.

Solution 15: Check for Antivirus Interference

Antivirus software can sometimes block SMTP connections. Temporarily disable your antivirus and try sending an email again.

Solution 16: Use Port 25, 465, or 587

Try using different SMTP ports. Port 25 is the standard SMTP port, but some providers might require the use of ports 465 (for SSL) or 587 (for TLS).

Solution 17: Review Your Account's Security Settings

Check your email account's security settings to ensure that nothing is blocking SMTP access.

Solution 18: Seek Professional Help

If all else fails, consider seeking professional help from an IT expert or your email provider's support team.

In conclusion, the "535 5.7.3 Authentication Unsuccessful" error can be caused by a variety of factors. By following the solutions outlined in this article, you should be able to narrow down and resolve the issue, allowing you to successfully send SMTP mail messages again.

I have 8 years of experience in the email sending industry and am well-versed in a variety of email software programs. Thank you for reading my website. Please feel free to contact me for any business inquiries.