Nice work! This is a great solution for something fully private and self-hosted. I'm building something in this space too (hosted, not self-hosted) and it's encouraging to see a clean open-source option for people who want full control.

For anyone reading who wants this but doesn't want to manage Docker/infrastructure: I'm working on a hosted alternative at https://mailbridge.app. Different tradeoff: you're trusting a third party with read-only credentials instead of running your own server. For those with the chops (or who want to learn the technical side a bit more), Magpie is probably the better fit.

Question for OP: are you handling deduplication for POP3 accounts that don't support UIDL? That's been the trickiest part for me so far.