Microsoft is phasing out Basic Authentication (the traditional username and password method) for third-party apps and services that use SMTP to send email. Support for basic authentication will be discontinued completely by September 2025.
This means if you’re using SMTP AUTH to send emails from your website or application, you’ll need to update your authentication method.
To continue using Microsoft email services for sending emails through third-party applications, you’ll need to switch to OAuth (Modern Authentication).
This post will explain:
- Why Microsoft is making these authentication changes
- How these changes might affect your email setup
- What steps you need to take to keep your emails sending without interruption
- What options you have moving forward
Is Your Email Setup Affected?
You’re likely impacted by these changes if you’re seeing SMTP authentication errors when sending email. This commonly occurs if you’ve configured basic SMTP settings using your Microsoft credentials in any of these scenarios:
- Website contact forms or automated notifications
- Applications that send transactional emails
- Hardware devices like printers or scanners that send email
- Custom integration using Microsoft’s SMTP servers
If you’re encountering issues, you might see error messages like this:
Error: 535 5.7.140 Authentication unsuccessful, basic authentication is disabled.
If you’re already using modern authentication methods (like OAuth 2.0) with your Microsoft 365 or Outlook integration, you won’t need to make any changes.
However, if you’re using basic SMTP authentication with your Microsoft username and password, you’ll need to update your configuration before September 2025, when Microsoft completely retires basic authentication.
How to Fix Microsoft SMTP Authentication Errors
If you’re dealing with these authentication issues, you have two options to resolve them so your emails keep sending.
1. Update to Modern Authentication
If you want to continue using your Microsoft email services, you’ll need to switch to Modern Authentication (OAuth 2.0).
This process requires software that supports OAuth 2.0, and you’ll need to set up special application permissions in your Microsoft account. Due to Microsoft’s deprecation of Basic Authentication, businesses using Office 365 SMTP directly (e.g., for email delivery via third-party tools) may run into issues unless those services support OAuth2 (Modern Authentication)
For WordPress users, there’s a simple solution available. The WP MAIL SMTP plugin includes a One-Click Microsoft 365/Outlook Setup feature that handles all the complex OAuth configuration automatically. You will find detailed instructions at https://wpmailsmtp.com/wordpress-smtp-settings/
You will need to purchase the PRO version at $99 per year for your WordPress website unless your website is hosted by Delta Digital. We have an Agency license to deploy the plugin to 100 websites. We currently manage 50 WordPress websites for our clients so there are still capacity. Basic WordPress Hosting starts at £40 per month. We offer a free migration service. Don’t wait for your website contact form to stop functioning!
