POP3 client in zoho not downloading email, non-zoho clients work fine

POP3 client in zoho not downloading email, non-zoho clients work fine

POP3 Email stopped downloading for some (but not all) of my team. It will download to outlook or thunderbird just fine, but not my pop3 client configured in zoho.I can send email  just not recieve. All settings checked and verified. Every test indicates the problem is in the interface or handshake between zoho and mail server. 

Zoho support has provided no help, just a phone call appt. from tech customer service and after verifying settings they say problem is on our end. My tech guys are more knowledgeable than the messenger Zoho provided for the call. They have verified and proven the issue is not with the mail server or the settings, it must be on Zoho's end, just need someone who understands zoho to look into it. There is a solution.

If we can't use email reliably from within Zoho, CRM is practically useless to us. Need some real tech support.
Thanks in advance.