As of a few days ago, we are not able to send email out of Zoho CRM to certain email addresses. We receive an error message:

"Please enter a valid To"

The issue appears to manifest only when trying to send emails that include a sub-domain as part of the address:

• Works just fine: example@example.com
• Produces the error: example@mail.example.com

This error started occurring with no changes made to our Zoho environment. We have sent multiple emails previously to email addresses that now manifest the error.

Thanks and please advise.