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.
I was using "Check mail from other accounts" to pull from 3 custom domain accounts into a single Gmail inbox. Tried auto-forwarding first. Within two weeks, my emails were landing in spam because the forwarding was tanking my sender reputation (it forwards the spam too). The Gmail mobile IMAP option is mobile-only with separate inboxes, so that was a non-starter.
I ended up building a hosted POP/IMAP bridge that does what Gmail used to do: logs into your external accounts on a schedule, fetches new messages, and forwards them to Gmail via SMTP with proper SPF/DKIM alignment. The key difference from auto-forwarding is pull vs. push. Spam stays on the external server instead of getting forwarded into Gmail.
It's at https://mailbridge.app. Currently collecting waitlist signups, polishing the MVP now. Happy to answer questions about the technical approach (credential encryption, deduplication, deliverability, etc).
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.