Zoho Recruit Emails bounce back

Hi,

We have recently seen a dramatic increase in the number of our sent emails to candidates and clients being blocked. The error messages are indicating that the Zoho IP address is blacklisted.

This is the first time we;ve seen this so not sure if this is a common problem, or if we should try and alter the emails addresses sitting in the background of Z Recruit? Although we send emails from our @companyname.co.uk in the background of Z Recruiit each user has a separate @zoho.com email address linked to Z Recruit. I wonder if this could be the problem?

Any help or advice would be really appreciated as this is very frustrating.