unable to send message;reason:could not connect to smtp host: smtpout.mail.zoho.com, port: 25, response: -1

unable to send message;reason:could not connect to smtp host: smtpout.mail.zoho.com, port: 25, response: -1

I have the message:

Unable to send message;Reason:Could not connect to SMTP host: smtpout.mail.zoho.com, port: 25, response: -1

Is the mail server down?