Unable to send message;Reason:Could not connect to SMTP host: smtpout.mail.zoho.com, port: 25, response: 452

Unable to send message;Reason:Could not connect to SMTP host: smtpout.mail.zoho.com, port: 25, response: 452

We are able to receive emails but unable to send emails. Any idea why this has happened? Has our email been blocked?

The error message

" Unable to send message;Reason:Could not connect to SMTP host: smtpout.mail.zoho.com, port: 25, response: 452"