If you're encountering the following error when attempting to send a notification via Gmail as an SMTP provider:

"Service Unavailable (503) - 535-5.7.8 Username and Password not accepted,"

it’s likely due to recent changes in Google’s security policies. Specifically, you may have been using Less Secure Apps (LSA) for authentication, which Google has discontinued. For more information, refer to Google’s official announcement:
Google Workspace Updates: Winding Down Google Sync and Less Secure Apps Support.

To resolve this issue, you need to create an App Password. Follow these steps to set it up:

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Steps to Create an App Password:

1. Enable Two-Step Verification
   Log in to your Google account and enable Two-Step Verification. This adds an extra layer of security and is required for generating an App Password. Learn more about enabling Two-Step Verification here:
   Google Two-Step Verification Guide.

2. Navigate to App Passwords
   Once Two-Step Verification is enabled, go to the App Passwords page in your Google account settings:
   App Passwords Page.

3. Generate an App Password

   • Select the app (e.g., “Mail”) and device (e.g., “Windows Computer”) for which the App Password will be used.

   • Click Generate to create the password. Google will provide a 16-character password.

4. Use the Generated Password
   Replace your existing Gmail password in your application or connector settings with the generated App Password. This ensures the authentication process adheres to Google’s updated security standards.

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Important Notes:

• Ensure your application or workflow is configured to use the new App Password instead of your regular Gmail password.

• Keep the App Password secure and avoid sharing it. If compromised, revoke it immediately through your Google account settings.

Following these steps should resolve the SMTP error and allow your notifications to send successfully.

For additional support, visit Google’s help page:
App Passwords Help.