If you use Google at this point for commercial services, you get what you deserve when they nuke your resources (caveat being services you cannot go elsewhere for, like an Android dev account). The evidence is robust they cannot be relied upon as a commercial services provider. Stop. using. Google.
(thoughts and opinions always my own, I am aware and understand in this context OP needs Google Cloud to integrate with customers in Google Cloud, which is very unfortunate, and so their Sisyphus task continues)
I run mine on a Pi4 no problem whatsoever, but I guess a VPS could also be used, although the scamalytics analysis will show it's a server or an IP shared with an anonymising VPN etc. if it's a shared IP on the host.
My second option would be Migadu, though I've not tried them myself yet (I have zero complaints with Purelymail and will use them for as long as they exist).
Another thing I kind of wanted to try is to run a basic mail server on my own hosts, and send the mail through a provider like Purelymail or something, for full control over storage and backups, has anyone here tried that?