Issue: Microsoft have turned off authenticated SMTP by default now for new users in the same organisation or new O365 organisations. New users now have to manually activate authenticated SMTP to be able to use this feature.

Fix Procedure:

1)The way to turn this feature on is via the O365 Portal > Users > Active Users. 
2)Click on a user account
3) Click on the mail tab and then click on Manage Email Apps:

4)Then turn on Authenticated SMTP by clicking the appropriate checkbox. 
This is only required for Email based accounts that need direct submission of SMTP like printers and scanners and obviously Wordpress sites.  Most other people are using MAPI or ActiveSync or OWA for submission.

Created by: Jason Kelton
Edited by: Rev Diaz