Mail with InfinityFree

if I understood correctly you don’t need to do anything special except set up MX records.
I guess they don’t limit you in any way in the sense that you have to use their products explicitly for email to work.



if you have some additional security records for email
try disabling them temporarily while you convince your self that the email works and then add things like DKIM, SPF, etc.

And definitely wait for DNS propagation before testing