Hi. I switched to ImprovMX using this guide and it works with my free subdomain. My email is [email protected] and it forwards to my Gmail account.
I have also set up an alias in Gmail so when I compose a new message I can select who the “From” email is. My choices are either my Gmail address or my fresh.infinityfreeapp.com address.
But all sending and receiving is done via Gmail.
The InfinityFree account I am using is a free subdomain but it is the only one on my InfinityFree account (e.g. it’s not another subdomain of my free account).