GNU Mailutils
	General-Purpose Mail Package	Official GNU Software

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1 Introduction

GNU Mailutils is a set of libraries and utilities for handling electronic mail. It addresses a wide audience and can be of interest to application developers, casual users and system administrators alike.

It provides programmers with a consistent API allowing them to handle a variety of different mailbox formats transparently and without having to delve into complexities of their internal structure. While doing so, it also provides interfaces that simplify common programming tasks, such as handling lists, parsing configuration files, etc. The philosophy of Mailutils is to have a single and consistent programming interface for various objects designed to handle the same task. It tries to use their similarities to create an interface that hides their differences and complexities. This covers a wide variety of programming tasks: apart from mailbox handling, Mailutils also contains a unified iterface for work with various DBM databases and much more.

The utilities built upon these libraries share that same distinctive feature: no matter what is the internal structure of an object, it is always handled the same way as other objects that do the same task. Again, the most common example of this approach are, of course, mailboxes. Whatever Mailutils program you use, you can be sure it is able to handle various mailbox formats. You even don’t have to inform it about what type a mailbox is: it will do its best to discover it automatically.

This approach sometimes covers entities which are seldom regarded as compatible. For example, using Mailutils it is possible to treat an SMTP connection as a mailbox opened only for appending new messages. This in turn, provides a way for extending the functionality of some utilities. As an example, using this concept of mailboxes, the usual mail delivery agent becomes able to do things usually reserved for mail transport agents only!

At the core of Mailutils is libmailutils, a library which provides an API for accessing a generalized mailbox. A set of complementary libraries provide methods for handling particular mailbox implementations: UNIX mailbox, Maildir, MH, POP3, IMAP4, even SMTP. Mailutils offers functions for almost any mail-related task, such as parsing of messages, email addresses and URLs, handling MIME messages, listing mail folders, mailcap facilities, extensible Sieve filtering, access control lists. It supports various modern data security and authentication techniques: TLS encryption, SASL and GSSAPI, to name a few. Mailutils is able to work with a wide variety of authorization databases, ranging from traditional system password database up to RADIUS, SQL and LDAP.

The utilities provided by Mailutils include imap4d and pop3d mail servers, mail reporting utility comsatd, general-purpose mail delivery agent maidag, mail filtering program sieve, an implementation of MH message handling system and much more.

All utilities share the same subset of command line options and use a unified configuration mechanism, which allows to easily configure the package as a whole.

This software is part of the GNU Project and is copyrighted by the Free Software Foundation. All libraries are distributed under the terms of the Lesser GNU Public License. The documentation is licensed under the GNU FDL, and everything else is licensed under the GNU GPL.

1.1 What this Book Contains

This book addresses a wide audience of both system administrators and users that aim to use Mailutils programs, and programmers who wish to use Mailutils libraries in their programs. Given this audience, the book is divided in three major parts.

The first part provides a detailed description of each Mailutils utility, and advices on how to use them in various situations. This part is intended for users and system administrators who are using Mailutils programs. If you are not interested in programming using Mailutils, this is the only part you need to read.

Subsequent parts address programmers.

The second part is a tutorial which provides an introduction to programming techniques for writing mail applications using GNU Mailutils.

Finally, the third part contains a complete Mailutils library reference.

This version of the book is not finished. The places that may contain inaccurate information carry prominent notices stating so. For updated versions of the documentation, visit http://mailutils.org/manual. All material that ends up in this document is first published in the Mailutils Wiki, available at http://mailutils.org/wiki. Be sure to visit it for latest updates.

If you have any questions that are not answered there, feel free to ask them at the mailing list bug-mailutils@gnu.org.

1.2 A bit of History, and why use this package?

This package started off to try and handle large mailbox files more gracefully then available at that time POP3 servers did. While it handles this task, it also allows you to support a variety of different mailbox formats without any real effort on your part. Also, if a new format is added at a later date, your program will support that new format automatically as soon as it is compiled against the new library.