Maddy Mail Server implements all functionality required to run a e-mail server. It can send messages via SMTP (works as MTA), accept messages via SMTP (works as MX) and store messages while providing access to them via IMAP. In addition to that it implements auxiliary protocols that are mandatory to keep email reasonably secure (DKIM, SPF, DMARC, DANE, MTA-STS).
It replaces Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC and more with one daemon with uniform configuration and minimal maintenance cost.
Full re-implementation in Go.
This library implements a simple "filesystem" inside an IMAP folder. The filesystem can be symmetrically encrypted (using the cryptography library's AES-128 Fernet construct), it supports concurrent readers/writers and file versioning. The motivation for this tool is that an IMAP account is the most commonly available form of standards compliant "cloud storage" available to the general public. This makes an IMAP account a compelling location for app backups or basic synchronization, and Mailfile's sister project, Mailpile, needs exactly such features.
FUSE compatible using fusepy.
Python v2.7, unfortunately.
The Debian project's canonical list of groupware available for Debian.
An utility written in Python that connects to an account on an IMAP server, recursively downloads everything, and stores the messages as mbox files. Useful for migration from system to system.
A shell script that turns a brand-new VPS or server into a mail server with a single command. Sets up webmail, IMAP, SMTP, a contacts application, a calendar, and even a web-based control panel for the whole shebang. Includes spam filtering, greylisting, backing up, and TLS certs for everything from Let's Encrypt. Even does virtual domains. No configuration during setup, and you can't really tweak the settings once it's up and running.