Zoho not processing our site's contact form emails, what could be wrong?

Zoho not processing our site's contact form emails, what could be wrong?

Since we switched to Zoho, messages sent via our site's contact form has stopped working, meaning, our guests emails have stopped getting to us. We use cloudflare DNS server and we've added Zoho's MX, SPF and DKIM records accordingly. Sending and receiving of emails on Zoho works perfectly, but our contact form has stopped working. What exactly do we need to do to get this to work?

Thanks in advance.
Josef