I have done all required SMTP configurations still i face problem in sending mails. 

Hi Sriharan,

The error ("550 5.2.1 Mailbox cannot be accessed") is an error sent back by outlook.com, not an error by the OutSystems Platform. It is possible you send the wrong credentials (username/password) or use the wrong "From" address?

Thank you,Kilian. I'll look on it.