@WHMCS SamP I contact the Microsoft Support and they sayed that is not a problem from Microsoft. They looked over my Settings in the Admin Panel from O365 and there looks all good.
Hey i setup WHMCS and Configure my SMTP Server from Office365. I get Cronjob Mails but i dont can send Mails over WHMCS. Like Invoice or something.
I get this Error: SMTP Error: data not accepted.
Here a Screen https://gyazo.com/c2ed7c414cb56a49785f26ae21ca2851