Well, yes. Obviously. If "they" compromise at a level below what we are capable of seeing - for example baseband controllers on every brand of motherboard that we own, then there's nothing we can do about it. There's nothing anyone can do about that, including the theoretical "run my own email server from home".
So I don't waste much sleep worrying about that case, because there's nothing I could about it. We do everything we can to ensure security - for example airgapped internal networks with physically separate switching hardware rather than VLANs to avoid the risk of compromised switch firmware.
If that's still too much risk for you, the choice is to get offline entirely. We're not in that business, we're in the business of providing a really usable email service with the best security protections that we can provide without compromising the usability to the point that people won't use it.