Unable to send mails via WordPress

Hi, I am using Zoho SMTP settings to send mail via my WordPress. My WordPress website will allow registrations, and whenever anybody registers it will send them a registration mail.

I have used WP SMTP Plugin to configure SMTP instead of PHP Mailer.

I have done the below settings

Host: smtp.zoho.com
SMTP Port: 465
Encryption: Use SSL encryption.
Authentication: Yes: Use SMTP authentication.
Username: admin@sitepandit.com
Password: xxxxxxxxxx

Whenever I am trying to send a test mail, it is showing below error.

SMTP -> get_lines(): $data was ""
2015-12-05 07:16:33 SMTP -> get_lines(): $str is "553 Relaying disallowed as SitePandit
"
2015-12-05 07:16:33 SMTP -> get_lines(): $data is "553 Relaying disallowed as SitePandit
"
2015-12-05 07:16:33 SERVER -> CLIENT: 553 Relaying disallowed as SitePandit
2015-12-05 07:16:33 SMTP ERROR: DATA END command failed: 553 Relaying disallowed as SitePandit
2015-12-05 07:16:33 SMTP Error: data not accepted.

Please confirm how to rectify the same.