The error is stating that you need to set authentication in the SMTP server. click 'account settings', scroll down left side to 'outgoing servers (SMTP) and click 'edit' for your SMTP server and set the authentication,

What should i ado in this, still getting error.

The error also mentions 'relay.' Click 'account settings' and on the account page, look at bottom row where it identifies the SMTP server. Is it showing that email address? The concern is that you have multiple addresses and each one must use its own SMTP server. Check to be sure that this account is using that SMTP server. Since the SMTP server description field has the email address, it should appear in that row of the account page. Otherwise, check with email provider to verify what specific authentication is required.