libquickmail is a library intended to give C/C++ developers a quick and easy way to send email from their applications. It supports multiple To/Cc/Bcc recipients and multiple MIME attachments without size limitation. It uses libcurl for SMTP communication, but a light version is also included without the libcurl dependancy. The library can also be used to just create a multipart MIME message body. It also comes with a command line application for sending mail (with optional attachments).
GNU Anubis is an SMTP message submission daemon. It represents an intermediate layer between the mail user agent (MUA) and mail transport agent (MTA), receiving messages from the MUA, applying to them a set of predefined changes, and finally inserting modified messages into an MTA routing network. The set of changes applied to a message is configurable on a system-wide and per-user basis. The built-in configuration language used for defining sets of changes allows for considerable flexibility and is easily extensible.
Clement is an email server application. Its main function is to block unwanted mail (spam) as soon as possible in the email exchange process. It accepts or rejects email while the SMTP session, initiated by the email sender, is still pending, accepting legitimate email messages without the need to return an error status to non-existent or "borrowed" return address later. Clement can operate in two modes, either as a standard MTA (as sendmail, Postfix, Exim, Exchange, etc.) to store email in the recipient's own area, or to transmit the mail to an another SMTP server acting as smart spam filtering device. Each email domain name Clement knows about can be treated in one of these two modes depending on the group to which the domain name has been set. Each message is verified by a virus scanner (ClamAV) while the SMTP connection is still open, but the refusal of mail and the reason for refusal is notified to the actual sender. Mail management is done via a Web interface and can be delegated to three administrative levels (Root-Admin, Group-Admin, Domain-Admin). Standard users can access their own logs (sent email status, email rejected, quarantined email, etc.). With this interface, the user can handle the rejection and acceptance of mail. Users who are level "Admin" can access the session logs (via the Web interface). Clement uses a SQL database (PostgreSQL, MySQL) to store and manage logs, user profiles, and dynamic management of directives concerning the sender-receiver relationship.
IndiMail is a messaging platform built using qmail and other messaging software. IndiMail has the ability to distribute the users in a domain across multiple hosts. IndiMail has multiple queues (called a queue collection), which can achiever very high concurrencies. The system IDs and configuration files used by IndiMail are all configurable through a set of environment variables, allowing you to customize IndiMail the way you want. IndiMail does not use hard-coded uid/gid in the executables, which makes it easy to distribute a binary package. IndiMail has features that any modern email server should have: SMTP, QMQP, QMTP, IMAP, POP3, DKIM, BATV, greylisting, filtering capability, and spam/virus control.
mxHero is a platform for email enhancing plugins. It features attractive real-time stats, security, policy, and monitoring capabilities. Email enhancement features include support for unlimited attachment sizes. It is compatible with all email systems and is currently deployed to over 5000 email accounts. The platform supports multiple domains, each with its own password.
Masqmail is an MTA (mail transport agent) for notebooks, workstations, home servers, and generally any host with no permanent network connection. It has special support for multiple transfer routes (e.g. to different mail providers). Address rewriting can be done in several ways. It is a slim replacement for full-blown MTAs such as sendmail, exim, qmail, or postfix and for the intended uses, configuration is much simpler.
Mireka is a mail server with SMTP, Mail Submission, and POP3 services. It can also be used as an SMTP proxy. As a proxy, it can help to prevent or diagnose mail problems, like outgoing backscatter spam. It provides detailed logging, basic mail traffic statistics, tarpit to prevent email harvesting, and loop detection. It can filter email by DNSBL, SPF, mail size, local domains, and recipients list. Local recipients can be specified using regular expressions. TLS is supported for incoming connections. Aliases, forward lists, and very simple mailing lists can be configured in XML. Custom filters and other components can be written in Java, and they can be easily implemented and installed.