Outlook can't get pop mail when connected via Frontier as ISP

Outlook can't get pop mail when connected via Frontier as ISP

I'm a new Zoho user. Configured Outlook on my laptop and it works fine when I'm on Wifi connected to Internet with Comcast as the ISP.
It also works fine if I connect to my AT&T Lte hotspot.

But if connected to Internet via Frontier as the Isp I get errors inOutllok send & receive that the pop and SMTP servers cannot be reached.

I can access Zoho via Web just fine with Frontier.

I called Frontier and they were unhelpful by saying I should be using their email.

I tried changing my DNS server to googles 8.8.8.8 instead of using FroniterDNS but no help.

Short of using a VPN, any idea what Frontier is doing and if I can work around it ?