Self-hostee storage for Gmail

Not sure if there's a pre-existing solution to this, so I figured I'd just ask to save myself some trouble. I'm running out of space in my Gmail account and switching email providers isn't something I'm interested in. I don't want to pay for Google Drive and I already self-host a ton of other things, so I'm wondering if there is a way to basically offload the storage for the account.

It's been like 2 decades since I set up an email server, but it's possible to have an email client download all the messages from Gmail and remove them from the server. I would like to set up a service on my servers to do that and then act as mail server for my clients. Gmail would still be the outgoing relay and the always-on remote mailbox, but emails would eventually be stored locally where I have plenty of space.

All my clients are VPN'd together with Tailscale, so the lack of external access is not an issue. I'm sure I could slap something roughshod together with Linux packages but if there's a good application for doing this out there already, I'd rather use it and save some time.

Any suggestions? I run all my other stuff in Kubernetes, so if there's one with a Helm chart already I'd prefer it. Not opposed to rolling my own image if needed though.