Error with SMTP setup for Zoho mail

Error with SMTP setup for Zoho mail

we are trying to setup SMTP plugin with ZOHO smtp details, but we are getting following error :

Checking your settings
Sending Test Email to   prasad@app.com
Email Status : Email Not Sent
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Debug Output :
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Connection refused

Your host has likely installed a firewall (REJECT packets) between you and the server. Ask them to open the ports. 
 
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