Mercury is free for non-commercial use, but for commercial users (including academic institutions and government bodies), there is a licensing fee. Licensed copies of Mercury are entitled to direct support from the author of the program.

More details here:

Version 4.8 was originally intended as a kind of "Version 5 dressed as version 4" release of Mercury. It has several significant new features that were originally flagged as V5 features, but because they are all quite fundamental, in the end I decided that it was fairer to release them in a way that would allow current v4.x licensees to gain access to them without requiring a new license. Over the course of its development, though, v4.8 has ended up taking on the feature list of a major release in its own right.

• OpenSSL  All Mercury modules that support secure connections using SSL/TLS now use the industry-standard OpenSSL libraries to do so. Using OpenSSL means greater interoperability with other sites, and allows the use of fully-signed certificates - indeed, Mercury even provides an easy, step-by-step generation process to create the CSR requests needed to purchase or acquire such certificates from online Certification Authorities.
• TCP/IP overhaul  The Mercury TCP/IP code, which is the core code that interacts with the Internet, has been totally overhauled. The main benefit of this comes with improved reliability and maintainability, which will make it easier to update the program in future - but you may also notice Mercury handling connections rather faster than in previous versions as well.
• Completely rewritten help system  Back in the days of Vista, Microsoft ceased supporting the ageing but functional WinHelp system, but failed to replace it with anything satisfactory (HTMLHelp, in particular, could not be used if the help file was installed on a shared volume, as Mercury frequently is). I finally completed my own help system in time to use it to host a completely reworked Mercury help file for this release. The new help system is up-to-date, consistently formatted, and much more usefully presented than the old version; it will also run properly no matter where Mercury is installed, or on what version of Windows it is running. The new system has a comprehensive table of contents and index, with free-text searching planned for future releases.
• SSL support in MercuryE  The MercuryE SMTP client now has comprehensive support for SSL connections in outgoing mail, and has an Access Control List that allows you to fine-tune connections and SSL usage for specific servers and domains.
• Direct-connect SSL support in MercuryS and MercuryP  The MercuryS SMTP server and MercuryP POP3 server now support direct-connect SSL, even though direct-connect SSL is formally deprecated by the Internet Standards Body. With the proliferation of low-quality cellphone mail clients, though, supporting direct-connect SSL has become unavoidable. Direct-connect SSL is turned off by default in both modules, but can be enabled in the 'SSL' settings page for each.
• Mercury IMAP search rewritten  The part of the Mercury IMAP server that implements searching has been completely rewritten: it should now handle any valid IMAP search expression (the old version had trouble with some operations) and should do it noticeably faster than the old version did.
• Mercury IMAP fixes and improvements   The MercuryI IMAP server has had numerous fixes and improvements made. Thunderbird users in particular should now find it works much better for them.
• DMARC support for mailing lists   DMARC is a convention used by a number of large sites, including Yahoo, which limits the hosts that can send mail for e-mail addresses in their domains. This plays merry hell with mailing lists, without providing any very good way of mitigating the problems. Mercury v4.8 does the best it can it encounters DMARC-restricted addresses in mailing lists, but our advice to you is the same as that of many other makers of mailing list management software - for the best experience using a mailing list, tell your subscribers to subscribe using an address that is NOT affected by DMARC.
• Many, many bug fixes   Behind the scenes there have been dozens of corrections made. While many of these were exotic and seldom-encountered, the overall effect is to improve the reliability and robustness of the program considerably.

As well as these features, Mercury now includes a commandline utility called HS.EXE which can be used to locate messages matching almost any header-based criteria very quickly and efficiently in directories containing large numbers of mail messages, such as spam repositories.

Although it was my intention that v4.73 be the last in the v4.x family of Mercury versions, at a certain point it became clear that there needed to be another update to fix a variety of small problems before beginning the migration to version 5. V4.74 contains over 40 small fixes, and two rather more significant corrections: a problem where messages deleted by IMAP-based clients were not actually deleted and reappeared on the next connection has been fixed; and an issue where a site had more than 3 MX mail servers declared but the first three were all unavailable (which could cause Mercury to attempt to connect to the wrong host for delivery) has also been addressed.

It's also worth noting that the Mercury installer and executable files are now digitally signed, using my name ("David Harris"). If your browser or installer complains about them being unsigned, or tells you that they have been signed with a signature that does not use my name, then the files are not authentic. A small security measure, but we believe it is quite worthwhile.

This is version 4.73 of Mercury/32. This release contains a lot of new functionality, as well as important fixes for a number of problems encountered in previous versions. Full release notes can be found here: 

The Mercury Mail Transport System is a Mail Server for Windows - a program that sends and receives mail on behalf of a group of users on a machine or local area network. Mail from the outside world is received by Mercury and placed in the addressee's mailbox, where the user can access it at any later point. Messages sent by local users to the outside world are passed to Mercury, which then takes whatever steps are necessary to deliver them, removing the burden from the user's workstation and allowing him to continue with other work

This is version 4.72 for WIndows environments, released in July 2009.

This release can be run as a native windows service which makes this version even faster.

A Mercury/32 Daemon is a plug-in module that extends the functionality of the system. Daemons are wired into Mercury's internal infrastructure at the lowest levels and have enormous power - using a Daemon, you can:

• Turn specific e-mail addresses on your server into automated mail processing engines

• Gain the opportunity to process every message that passes through your queue

• Add entirely new functions to the Mercury environment

• Extend existing protocol modules, by adding, changing or suppressing their commands

• Add completely new protocol layers to the program

• ... and much more.

Mercury makes a huge range of internal functions and data structures available to Daemons, all of which are documented in detail with working code samples in this kit.

To develop Daemons, you will need this kit, a programming environment (Microsoft Visual C++ and Borland C++ are explicitly supported, while other environments such as Delphi can be used with some effort), and some basic experience in writing Windows programs in C or C++.

The Mercury Mail Transport System is a Mail Server - a program that sends and receives mail on behalf of a group of users on a machine or local area network. Mail from the outside world is received by Mercury and placed in the addressee's mailbox, where the user can access it at any later point. Messages sent by local users to the outside world are passed to Mercury, which then takes whatever steps are necessary to deliver them, removing the burden from the user's workstation and allowing him to continue with other work

The Mercury Mail Transport System is a Mail Server - a program that sends and receives mail on behalf of a group of users on a machine or local area network. Mail from the outside world is received by Mercury and placed in the addressee's mailbox, where the user can access it at any later point. Messages sent by local users to the outside world are passed to Mercury, which then takes whatever steps are necessary to deliver them, removing the burden from the user's workstation and allowing him to continue with other work.

This version of Mercury/32 runs on Windows and includes support for NetWare.

Lukas Gebauer's proven SpamHalter Bayesian Spam Filtering technology and antiviral technology ClamWall is now included as a standard part of the Mercury distribution.

Mercury/32 v4.52 is a security patch release, addressing a serious weakness in the MercuryS SMTP server (specifically, a buffer overflow vulnerability in the way the server processes the AUTH command). All v4.x versions of Mercury earlier than v4.52 are vulnerable to this exploit, and users should regard the upgrade to v4.52 as mandatory.

V4.52 also fixes and extends the "Save attachment to file" filtering rule action (the "Set" button now works correctly, and you can now specify either a filename or a directory as the destination for the rule), and corrects a problem in the IMAP server where attempts to create folders using characters outside the supported character set might cause crashes.

A patched version of MercuryS suitable for use in Mercury v4.01c systems is available at as well as a patch for Mercury/NLM adressing the security issue with the MercuryS AUTH exploit for sites who do not wish to upgrade to v4.5, but we strongly urge making the move to v4.5x as soon as possible.

The feature set for v4.52 is the same as for v4.51, the release information for which is at: http://community.pmail.com/pmail/MercuryReleaseNotes.aspx

Although the manual is part of the release package, we offer the manual for separate download and viewing.

The Mercury Mail Transport System is a Mail Server - a program that sends and receives mail on behalf of a group of users on a machine or local area network. Mail from the outside world is received by Mercury and placed in the addressee's mailbox, where the user can access it at any later point. Messages sent by local users to the outside world are passed to Mercury, which then takes whatever steps are necessary to deliver them, removing the burden from the user's workstation and allowing him to continue with other work.

This version of Mercury/32 runs on Windows and includes support for NetWare.

Lukas Gebauer's proven SpamHalter Bayesian Spam Filtering technology and antiviral technology ClamWall is now included as a standard part of the Mercury distribution.

The Mercury/32 v.451 manual in PDF format is included with this distribution.

This is the official manual for Mercury Mail Transport version 4.01

The Mercury Mail Transport System is a Mail

Server - a program that sends and receives mail on behalf of a group of

users on a machine or local area network. Mail from the outside world is

received by Mercury and placed in the addressee's mailbox, where the user can

access it at any later point. Messages sent by local users to the outside world

are passed to Mercury, which then takes whatever steps are necessary to deliver

them, removing the burden from the user's workstation and allowing him to

continue with other work