Sent emails from zoho not arriving at destination (Comcast account)

Sent emails from zoho not arriving at destination (Comcast account)

I recently set up a new zoho mail account. I can send and receive emails fine except when I try and send emails to my Comcast account as a test. The emails never arrive and I made sure @zoho.com is not blocked by Microsoft Outlook which I use to access my Comcast (Pop3) email. The sent emails are not bounced back to Zoho, they simply never arrive in my Comcast account. Yes, I checked the SPAM folder and am very familiar with email procedures.