Bichon is an open-source email archiving system that synchronizes emails from IMAP servers, indexes them for full-text search, and provides a REST API for programmatic access. Unlike email clients, Bichon is designed for archiving and searching rather than sending/receiving emails. It runs as a standalone server application that continuously synchronizes configured email accounts and maintains a searchable local archive. Built in Rust, it requires no external dependencies and provides fast, efficient email archiving, management, and search through a built-in WebUI. Its name is inspired by the puppy my daughter adopted last month.

github.com, in "rustmailer/bichon: Bichon – A lightweight, high-performance Rust email archiver with WebUI"

This was very straightforward to setup and now syncs / backups two of my mail accounts. Although syncing a google mail account is a bit of a PITA, as it requires to setup a custom Google Cloud application along with an OAuth client.