Alot is a terminal-based mail user agent based on the Notmuch mail indexer. It is written in Python using the urwid toolkit and features a modular and command prompt driven interface to provide a full mail user agent (MUA) experience as an alternative to the Emacs mode shipped with Notmuch.

Technology for Resting Email Encrypted Storage (TREES) is a NaCL-based Dovecot encryption plugin. This plugin adds individually encrypted mail storage to the Dovecot IMAP server. It is inspired by Posteo's scrambler which uses OpenSSL and RSA key pairs. TREES works in a similar way, but uses the Sodium crypto library (based on NaCL).

How it works:

1. On IMAP log in, the user's cleartext password is passed to the plugin.

2. The plugin creates an argon2 digest from the password.

3. This password digest is used as a symmetric secret to decrypt a libsodium secretbox.

4. Inside the secretbox is stored a Curve25519 private key.

5. The Curve25519 private key is used to decrypt each individual message, using libsodium sealed boxes.

6. New mail is encrypted as it arrives using the Curve25519 public key.

OpenSMTPD is an implementation of server-side SMTP, with some additional standard extensions. It allows ordinary machines to exchange e-mails with other systems speaking the SMTP protocol, or to deliver them to local users.

In order to simplify the use of SMTP, OpenSMTPD implements a smaller set of functionality than those available in other SMTP daemons. The objective is to provide enough features to satisfy typical usage at the risk of unsuitability to esoteric or niche requirements.

This program can pull, and send, email and labels (and changes to labels) from a GMail account and store them locally in a maildir with the labels synchronized with a notmuch database. The changes to tags in the notmuch database may be pushed back remotely to your GMail account.

Rspamd is a spam filter that evaluates email messages by a number of rules including: regular expressions, statistical analysis, and URL blacklists. Rspamd gives each message a spam score, e.g., for further processing by an MTA.

neatmail is a noninteractive mail client. It generates a listing of the messages in a mailbox in mbox format and executes a list of ex-like commands on it.

Email::Sender replaces the old and sometimes problematic Email::Send library.

Swaks is a flexible, scriptable, transaction-oriented SMTP test tool. It handles SMTP features and extensions such as TLS, authentication, and pipelining; multiple versions of the SMTP protocol including SMTP, ESMTP, and LMTP; and multiple transport methods including unix-domain sockets, internet-domain sockets, and pipes to spawned processes. Options can be specified in environment variables, configuration files, and the command line allowing maximum configurability and ease of use for operators and scripters.

notifymuch displays desktop notifications for messages in the notmuch database. The notifications are sent using libnotify to a notification daemon. The query to find messages to send a notification about is configurable, and a notification for the same message will not be send within a configurable period (defaults to 48 hours). To use notifymuch, run notifymuch after new mail is indexed, this can be automated by invoking notifymuch from the post-new hook.

Mairix is a program for indexing and searching email messages stored in Maildir, MH, MMDF or mbox folders.

mpop is a small and fast POP3 client suitable as a fetchmail replacement.

mpop supports multiple accounts, header based mail filtering, delivery to mbox files, maildir folders or an MDA, TLS/SSL, several authentication methods, IDN and SOCKS proxies.

The Libpst utilities include readpst which can convert email messages to both mbox and MH mailbox formats, pst2ldif which can convert the contacts to .ldif format for import into LDAP databases, and other tools to process Outlook email archives.

Email::MIME::ContentType parses a MIME Content-Type header.

Postorius is a Django app which provides a web user interface to access GNU Mailman.

Khard is an address book for the console. It creates, reads, modifies and removes CardDAV address book entries at your local machine. For synchronizing with a remote address book, vdirsyncer is recommended. Khard can also be used from within the email client mutt.

Anubis is a daemon that sits between the Mail User Agent (MUA) and the Mail Transfer Agent (MTA). When a mail is sent by a user in the MUA, it is first passed to Anubis, which performs additional processing to the message before passing it on for delivery by the MTA. Anubis may, for example, modify the message headers or body, or encrypt or sign the message.

Email::Date::Format provides a means for generating an RFC 2822 compliant datetime string.

This package provides Python bindings to use the Notmuch mail indexing and search library.

Bogofilter is a mail filter that classifies mail as spam or ham (non-spam) by a statistical analysis of the message's header and content (body). The program is able to learn from the user's classifications and corrections. It is based on a Bayesian filter.

The filter-dkimsign OpenSMTPd filter signs outgoing e-mail messages with DKIM (RFC 4871).

Nullmailer is a simple replacement MTA for hosts that receive no local mail and only relay mail to a fixed set of smart relays. It's useful for systems such as Web servers that must be able to send email notifications, without having to run a full-blown MTA such as sendmail or qmail.

Nullmailer is designed to be simple to configure, easy to extend, and secure. It requires little ongoing administration. The included sendmail emulator front-end should allow most (if not all) sendmail-compatible programs to run without any changes.

This is a Python library for the generation of email authentication headers. The library can perform DKIM, SPF, and DMARC validation, and the results are packaged into the Authentication-Results header. The library can DKIM and ARC sign messages and output the corresponding signature headers.

The hyperkitty Django app provides a web user interface to access GNU Mailman3 archives, and manage it. This interface uses django, and requires some configuration.

Dovecot is a mail server whose major goals are security and reliability. It supports mbox/Maildir and its own dbox/mdbox formats.