E-mail from Google and Hotmail don't come through, but only when using a contact form

E-mail from Google and Hotmail don't come through, but only when using a contact form

I have a contact form that just uses a simple php mail script that sends an email to one address on my Zoho account. If I use a "from" email address on the contact form from any domain other than @gmail.com or @hotmail.com, the emails come through fine. I've tried several different Gmail accounts but the emails still don't come through.

I can send an email to the Zoho email address from any Gmail account from gmail.com and those come through fine.

Are there any logs I can check to see what may be happening? What would be the best way to troubleshoot this?