## 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.