Securing the privacy of email relays with different providers (protonmail and gm

[kalpana]

I'm trying to secure the privacy of an email address and email relay network. I'm using protonmail as my service provider and I have a custom domain. It's purpose is to be the point of contact for the one and only site admin for a rudimentary Django blog CMS for some boring academic philosophy content. The project is in the testing stage currently. Only once the project goes into production will the custom email address be published publicly. I am anticipating very low traffic. I don't plan on logging into my protonmail account to check for messages regularly. So if I set up a relay, so that all protonmail messages are forwarded to a different email (say a less secure common gmail account that I do check several times a day), how easy would it be for a bad actor to be able to track the relay from a protonmail-based account to a regular gmail account?

I don't have adversaries and I can't imagine ever being the target of an attack. So there isn't much risk. But hypothetically speaking, for a bad actor as highly sophisticated as, say, an advanced professional pen-tester, how realistic would it be for them to identify the destination gmail address based on emails coming from the originating protonmail account?