Troubleshooting GMAIL SMTP authentication errors

Many websites use PHP to send email via SMTP. For example, you could create a custom mail form, or use a WordPress SMTP plugin. 

• How do I send PHP mail via SMTP?
• PHPmailer overview
• Configuring the 'WP Mail SMTP' plugin

A problem you will run into is that Google's security settings do not allow you to send via SMTP through their servers unless you explicitly allow this. There are two ways to allow your application to send SMTP mail through GMAIL.

The first option is to enable 'Less secure apps' within GMAIL.

1. Log into your GMAIL account.
2. Navigate to the 'Less secure apps' page.
3. Toggle to turn this feature 'ON'.
4. Wait at least 1 hour for Google to update this setting.
5. Test your mail application again. It should now send correctly via SMTP.

A more secure option is to enable OAuth 2.0 authentication for your application.

• https://developers.google.com/gmail/api/auth/about-auth

Please note that support is unable to assist with this custom configuration.