Tickets mail blocked. Service unavailable; Client host [sender4-zs8.zoho.com] blocked by dnsbl.sorbs.net; Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?136.143.188.8

Hello, our Zoho Desk emails are being blocked with the message:
Service unavailable; Client host [sender4-zs8.zoho.com] blocked by dnsbl.sorbs.net; Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?136.143.188.8

Can you please get this resolved?