I am not able to setup Outgoing Mail Server with Microsoft Business Mail Server. Below is the information I typed in:

SMTP Server: smtp.office365.com

SMTP Port:587

Connection Security: TLS(STARTTLS)

username: XXXXX@XXXXXXXXXX.onmicrosoft.com

Password: The password

When I perform "Test Connection", the error message I received is:

Connection Test Failed! Here is what we got instead:

 535

5.7.3 Authentication unsuccessful [HK0PR01CA0072.apcprd01.prod.exchangelabs.com]

I tired replacing username with my actual email but it still fails with the same error message.

Note: I tried using another email address under Google (with Google App Password enabled) and successfully pass through "Test Connection". 

Please help to share with me how I should properly setup outgoing mail server connection with Microsoft Business Mail Server. Thank you very much !