Free Mail Servers
Free and Open Source Email Servers / Mail Transfer Agents
Free Mail Servers
The free mail servers (sometimes called Mail Transfer Agents, or MTA for short) on this page allow you to transmit email from one computer to another, using something called the Simple Mail Transfer Protocol, or SMTP for short. For example, it can receive email from an email client (software) and send it to another system. They can also allow email clients to retrieve its stored messages using either the Post Office Protocol, or POP3 for short, or the Internet Message Access Protocol, or IMAP. The email servers can either deliver the messages directly to the destination (end-to-end delivery) or relay them to another mail server for further transmission.
Please note the following:
The programs mentioned on this page are not for the ordinary email user. If all you want is a computer program that allows you to read and write email, please see the Free Email Clients page instead. On the other hand, if you want free email services (like webmail or the like), please go to the Free Email, Webmail, and Email Forwarding page.
Note that some of the software packages listed below are noted as being available only as source code. For non-programmers, in plain English, this means that the programs are distributed in a form that cannot be run directly on your computer. It has to be converted into a machine-readable form using a process known as "compilation" — that is, in programming lingo, you will need to "compile the program" before it can be used. For most non-programmers who only want to set up and use a program rather than muck around with technical stuff, this basically implies that you should probably skip that particular piece of software and look for another one that comes with a ready-to-run package.
Free Mail Servers (Email Servers / Mail Transfer Agents)
- hMailServer (Windows)
This mail server for Windows, hMailServer, supports the SMTP, IMAP and POP3 email protocols. It also includes a score-based spam filtering system (SpamAssassin) and can be integrated with antivirus software (to scan incoming and outgoing email). Other features include support for server-side rules, SSL, multihoming, virtual domains, routing, built-in backup, etc.
- Mercury Mail Transport System (Windows, Novell NLM)
Mercury supports the following protocols: SMTP, POP3, IMAP (IMAP4rev1), SSL (for SMTP, POP3 and IMAP), PopPass, HTTP (for mailing list management), finger and PH (for directory lookups). It can handle multiple domains on one system, supports aliases, autoresponders, forwarding, filtering, Bayesian spam filtering, mailing lists, multiple queues, domain mailboxes (that receives all mail sent to a particular domain), customisable ("customizable" in US English) notifications (such as delivery failure messages), greylisting, relaying, killfiles, blocklists, full session logging, the ability to listen on multiple ports, the ability to relay messages via SMTP or use full end-to-end delivery, the ability to restrict which connections are allowed (based on address range), etc. (This is just a subset of the list of features available: the full list is too long to mention here. Please see their site or documentation for details.) This mail server is only free for private or non-profit use.
- Apache James (Windows, Mac OS X, Linux)
Apache James is a mail transfer agent ("MTA") that implements POP3 and SMTP. IMAP support has been added to the version 3 series of the software, which, at the time I write this, is still under development. The software can also function as an NNTP news server. The software is written in Java, which means that it can run on any system that has a Java Virtual Machine installed.
- Citadel (Linux)
Citadel is actually a groupware program (with instant messaging, bulletin boards, shared calendars, mailing list server, etc), but it is listed here because it includes an email server. It supports ESMTP, POP3, and IMAP, and also includes a webmail interface. Access to your email over TLS/SSL is also supported. It has built-in spam filtering with support for things like blacklists, SpamAssassin, and an antivirus. Binary packages for Debian/Ubuntu Linux are available. For all other Linux users (or perhaps also users of other Unix type systems, including Mac OS X), you will need to compile the program yourself from the source code.
- Postfix (Unix-type systems) (Source code only)
Postfix is a mail transfer agent with support for SMTP, DKIM, DomainKeys, SenderID, TLS encryption and authentication, junk email filtering, etc.
- qmail (Unix-type systems) (Source code only)
This software, qmail, is an SMTP server for Unix-based systems like Linux (and presumably also Mac OS X). It was written to be a secure replacement for sendmail (another mail server). It also provides a POP3 service.
- Sendmail (Unix-type systems) (Source code only)
Sendmail supports SMTP, ESMTP, UUCP, etc. It is known (or perhaps more accurately, notorious) for being hard to configure, the result of its attempt to provide the administrator with the ability to control many things.
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