Balsa is a highly configurable and robust mail client for the GNOME desktop. It supports both POP3 and IMAP servers as well as the mbox, maildir and mh local mailbox formats. Balsa also supports SMTP and/or the use of a local MTA such as Sendmail.

Email::MIME is an extension of the Email::Simple module, to handle MIME encoded messages. It takes a message as a string, splits it up into its constituent parts, and allows you access to various parts of the message. Headers are decoded from MIME encoding.

MHonArc is a Perl mail-to-HTML converter. MHonArc provides HTML mail archiving with index, mail thread linking, etc; plus other capabilities including support for MIME and powerful user customization features.

Mail::AuthenticationResults parses the message header field that indicates the message authentication status as per RFC7601. This module is not fully compliant with the RFC but it tries to implement most styles of Authentication-Results header seen in the wild.

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.

A flexible, extensible mail retrieval system with support for POP3, IMAP4, SSL variants of both, maildirs, mboxrd files, external MDAs, arbitrary message filtering, single-user and domain-mailboxes, and many other useful features. This is a fork derived from getmail 5.14, aimed at Python 3 compatibility.

Alpine is a text-based mail and news client. Alpine includes several tools and applications:

1. alpine, the Alpine mailer

2. pico, the standalone text editor, GNU nano's predecessor

3. pilot, the standalone file system navigator

Mail::DKIM is a Perl module that implements the DKIM standard, and the older Yahoo! DomainKeys standard, both of which sign and verify emails using digital signatures and DNS records. Mail-DKIM can be used by any Perl program that wants to provide support for DKIM and/or DomainKeys.

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

Cyrus IMAP is an email, contacts and calendar server. It provides support for a variety of protocols including JMAP, IMAP/IMAP-S, and POP3/POP3-S as well as CalDAV and CardDAV.

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.

This module wraps MIME::Base64 and MIME::QuotedPrint.

Claws-Mail is an email client (and news reader) based on GTK+. The appearance and interface are designed to be familiar to new users coming from other popular email clients, as well as experienced users. Almost all commands are accessible with the keyboard. Plus, Claws-Mail is extensible via addons which can add many functionalities to the base client.

Birdtray is a free system tray notification for new mail for Thunderbird/Icedove. Its features include an unread mail counter, snooze-able new mail notifications, configurable fonts for different accounts, a ``quick compose'' function with pre-configured templates, and a direct connection to the Thunderbird database, making it completely independent from the extension API.

msmtp is an SMTP client. In the default mode, it transmits a mail to an SMTP server (for example at a free mail provider) which takes care of further delivery.

This project is a reimplementation of the Python stdlib smtpd.py based on asyncio.

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.

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.

libESMTP is an SMTP client that manages posting (or submission of) electronic mail via a preconfigured MTA.

It may be used as part of a MUA, or other program that must be able to post electronic mail where mail functionality may not be that program's primary purpose.

libESMTP's high-level API shields developers from the complexity of SMTP. It transparently handles many SMTP extensions including authentication, TLS, and PIPELINING for performance. Even without a pipelining server, libESMTP offers much better performance than would be expected from a simple client.

CRM114 is a system to examine incoming e-mail, system log streams, data files or other data streams, and to sort, filter, or alter the incoming files or data streams according to the user's wildest desires. Criteria for categorization of data can be via a host of methods, including regexes, approximate regexes, a Hidden Markov Model, Orthogonal Sparse Bigrams, WINNOW, Correlation, KNN/Hyperspace, or Bit Entropy (or by other means--it's all programmable).

This package provides a CLI application to execute scripts on IMAP mailbox changes (new/deleted/updated messages) using IDLE and it is mostly compatible with the configuration of imapnotify made with Python.

pan is a Usenet newsreader that's good at both text and binaries. It supports offline reading, scoring and killfiles, yEnc, NZB, PGP handling, multiple servers, and secure connections.

isync/mbsync is a command-line tool for two-way synchronization of mailboxes. Currently Maildir and IMAP are supported types.

The osmtpd API is an event-based C programming interface for writing OpenSMTPd filters.