Pegasus Mail

Mercury/32 v4.01a (December 2003)

V4.0, while a long time coming, includes some of the most powerful improvements we have ever made to Mercury, and creates a significant roadmap for future versions. In particular, the MercuryB web server protocol module heralds the arrival of web-based management and services for Mercury, and the inclusion of SSL support improves security dramatically.

MercuryB HTTP server: this new protocol module implements the HTTP protocol for web-based access using a loadable service module approach to provide services. MercuryB is not intended as a general-purpose web server - it is specifically targeted at tasks specific to Mercury, such as mailing list subscription management (included in this release), remote administration and web mail (in development).

SSL/TLS support The MercuryS (SMTP server), MercuryP (POP3 server) and MercuryI (IMAP4 server) protocol modules now have comprehensive, easy-to-enable support for the SSL secure sockets protocol.

Web-based mailing list subscription management Using the new MercuryB HTTP server, mailing list subscribers can now manage their list subscriptions over the web. Subscribing, unsubscribing and managing subscriptions is now as easy as using a web browser and filling in some simple forms.

Heavily improved spam filtering The content control engine in Mercury/32 v4.0 has been heavily enhanced with new tests and a new default rule set that catches vastly more spam. We are also currently developing auto-update mechanisms that will allow spam rule sets to be updated automatically, allowing faster response to new types of spam as it arises. The content control engine now also has more options for adding headers to messages and can generate diagnostic headers indicating which rules contributed to the calculated weight for the message. Mercury's autoreply engine has also been changed so that any message getting a positive content control weight will not receive an autoreply: this prevents the server from sending autoreplies in the majority of cases.

Improved HTML and encoding handling in Content Control Mercury's content control engine has been retrofitted with improvements made in Pegasus Mail v4.12, and now only checks textual components of messages. When doing so, it now correctly applies BASE64 and Quoted-printable decoding before applying its tests, and strips HTML tags from HTML content (leaving only A, IMG and base tags for later testing). Content control now has explicit tests that check for lazy HTML (IMG tags with remote references), IFRAME tags, and excessive numbers of comments. The regular expression engine has also been extended with a number of powerful new tests.

Attachment filtering Mercury's general-purpose filtering rule engine has been enhanced with the ability to filter attachments within messages. Attachment filters can work on the filename or extension of the attachment, and can delete attachments from messages if required. The filtering engine now also has an action that can add a header of your choosing to any message as it is processed.

VERP support in mailing lists VERP (variable envelope return processing) allows near-total automation of error processing in mailing lists. Mercury/32 now includes three modes for handling mailing list errors, two of which use VERP. For larger lists, VERP can substantially reduce the amount of effort required to keep subscriber lists up-to-date.

Subscription passwords You can now specify that a password be required for subscription to a mailing list - this eliminates casual or unwanted subscriptions to mailing lists and reduces moderator workloads.

MercuryI IMAP Server improvements The IMAP4 server has been heavily overhauled and is now much more robust than in previous versions. Sites using stateless clients (such as webmail packages like Twig or IMP) should notice performance improvements as well.

Transaction-level filtering in MercuryS The MercuryS SMTP server now supports filtering at the transaction level - you can apply expressions to the SMTP EHLO command and to the data of the message as it is actually received. This is an incredibly powerful feature, particularly for dealing with address harvesters and spammers who attempt to relay via your server.

Short-term blacklisting MercuryS now supports the idea of short-term blacklisting, where clients that breach too many compliance conditions or match specific transaction-level filters can be blocked from connecting to the server for a period of 30 minutes. This is a powerful way of dealing with zombie systems (computers that have been taken over by hackers or spammers) and of protecting against denial-of-service attacks.

Connection control overhauled The ability of the Mercury server modules to control which machines can connect to them based on IP address has been totally overhauled. It is now possible to specify arbitrary address ranges to which restrictions can be applied, and each restriction can have specific attributes enabled or disabled (so, for instance, you could create an "Allow" entry that permitted a system to relay mail through MercuryS but which was not exempt from transaction-level filtering).

Improved console output The various Mercury server protocol modules now produce much more detailed information on the console and in the log files to show why particular actions occurred.

Progressive backoff in delivery You can now tell Mercury to use a "progressive backoff" algorithm when calculating retries for mail jobs; this tells Mercury to start with a relatively short retry period, then use gradually longer and longer retry periods the more retries occur. This can dramatically speed the delivery of mail when one-off transient glitches occur, and cuts down queue congestion caused by messages with more significant delivery problems.

Click here to go to the downloads page, where you can retrieve the Mercury/32 v4.01 release archive.