I don’t know of a free relay, but here’s how I do it:
5€ hetzner VPS with Proxmox Mail Gateway installed, relays e-mail to my residential IP. To deal with my IP changing every now and then, I have 2 scripts:
One at home updates my A record on cloudflare when an IP change is detected
One on my PMG that checks for my A host on cloudflare and if the IP changes, modifies the conf files where the my residential IP is set then restarts postfix.
I don’t know of a free relay, but here’s how I do it:
5€ hetzner VPS with Proxmox Mail Gateway installed, relays e-mail to my residential IP. To deal with my IP changing every now and then, I have 2 scripts:
Been working great for 2 years now.