Why do I see "Email Error" while sending emails from Graphus?

When integration with Graphus is enabled, all users/targets in an organization should be Microsoft licensed users which can be viewed on the following location: https://cloud.graph.us/orgUsersLicense?licenseType=protected. 

Emails will not be delivered to unlicensed Microsoft users. BullPhish ID campaign emails will only be delivered to licensed Microsoft users.

BullPhish ID team is working on a solution to automatically inactivate organizations with unlicensed users. This is to ensure that MSPs can continue sending their campaigns through SMTP service where whitelisting is required. This information is also available in the article BullPhish ID integration with Graphus.