Error "Invalid login: 535 5.7.139 Authentication Unsuccessful"

[travis.evers]

Overview

A failed notification message is received with the following error:

Error sending email: Invalid login: 535 5.7.139 Authentication unsuccessful, user is locked by your organization’s security defaults policy.

Cause

This particular error is returned directly by the Microsoft/Outlook SMTP provider. It is likely not to have permissions in the credentials being sent in the SMTP Provider since it rejects the request.

Solution

Please contact Outlook/SMTP Provider admin, and please see a few references from Microsoft on this error:

• Problem with authenticating user for outgoing mail with WP Mail SMTP
• 535 5.7.139 Authentication unsuccessful