Emails via contact form fail when using Cloudflare DNS

Emails via contact form fail when using Cloudflare DNS. Other websites I have not moved are not affected. I’ve turned off Proxy on WWW in case.

Website points to Office 365 email (which works fine).
Pages like Contact form don’t email out.
We use DMARC and DKIM and SPF records.

Only the contact form part doesn’t work.
Yet another website without Cloudflare proxy works fine.
Are there extra settings for Cloudflare that need to be set up?

Dmarc reject changed to quaruntine whilst we are working on a fix