Zoho not processing web site contact form emails

Zoho not processing web site contact form emails

Since switching to zoho, I stopped getting messages sent via my site's contact form. The site host uses php to send mail so I assume I have to authorize them to send on my behalf.  So I added the zoho mx record to my site host's cpanel and their ip and domain wherever I could at zoho. That seemed to work for a while but now it's failing again.
What exactly do I need to do to get this to work?