How do I enabled smtp auth for a mailbox in exchange online

Hi All,

     I am trying to enable SMTP auth for my exchange server.  I have followed the instruction given here 

https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission

to enable a specific mailbox to have SMTP Auth. But I am still getting a timeout error when I am trying to test the config via smtper.net I also tried writing a simple c# code and test getting the same issue. Here are the config that I used

Host: smtp.office365.com

port: 587

using secure connection and authentication using the username and password of the user account

Please help

Thanks

Tiklu