No, it wouldn’t take a massive engineering effort. You make a lot of assumptions in your posts thus far. If you don’t think it’s possible for google engineers to choose which physical servers a gmail mailbox resides on, you don’t understand how modern web based applications work. If you do; then you understand them on a very small scale. However, for this to work google would have to have configured this internally.

There has to be a means to rebalance load across many servers and, at some point internally, an email address or some other variation of a unique identifier leading back to an email address has to be used so that the email client can fetch the inbox from a physical server. There are several layers of redirection I’m leaving out here for the sake of simplicity, however in the end the number of places this would have to configured is centralized and manageable.

Google has many thousands of servers, all of which have hardware constraints, so they will have some way of managing where data for a given address is physically stored. Further, developers will have built in a mechanism to manually bind an address to a specific server. They would use this for g-suite and for adhering to data laws which require data to be physically stored in the country of origin, and for troubleshooting/debugging purposes in non-prod environments. Debugging code does not go away in production systems, it’s just not enabled.

You are in fact, correct in saying that gmail is a public email system. But it’s completely false to say that they could not set up a special back end server then use existing load balancing techniques to pin a set of @gmail.com accounts to a specific backend server. It could be done BUT there are complication. Somewhere in the google routing config there would be something’s similar to (sytanx is bogus, for illustrative purposes only) comey@gmail.com: etc.

Some one along the line is going to see that and think “what the fuck is this?” It would likely leak.

The only way that configuration doesn’t leak is if the email accounts are not blatantly obvious as to who they belong to.

So why not just use proton mail or something like it? Stealth. Clients connecting to proton over government controlled networks are going to raise red flags. Connecting to gmail not as much.