The limit is not on the number of email addresses, but on the number of characters in the “To” address field. You can enter up to 200 characters in Notification email field.
If this does not suffice, consider creating an email distribution list on your mail server and using that address in your Caspio form. A distribution list is a feature that allows a user to maintain a list of email addresses and send messages to all of them at once. Usually your company’s system administrator can set up email distribution list. If you use free email accounts such as Gmail or Yahoo, you can search online to find how they provide forwarding to multiple addresses option.