procmail is an

email Electronic mail (usually shortened to email; alternatively hyphenated e-mail) is a method of transmitting and receiving Digital media, digital messages using electronics, electronic devices over a computer network. It was conceived in the ...

server software component — specifically, a message delivery agent (MDA). It was one of the earliest mail filter programs. It is typically used in

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

mail systems, using the

mbox Mbox is a generic term for a family of related file formats used for holding collections of email messages. It was first implemented in Research Unix, Fifth Edition Unix. All messages in an mbox mailbox are Concatenation, concatenated and store ...

and

Maildir The Maildir e-mail format is a common way of storing email messages on a file system, rather than in a database. Each message is assigned a Computer file, file with a unique name, and each mail folder is a file system directory containing these fil ...

storage formats. procmail was first developed in 1990, by Stephen R. van den Berg. Philip Guenther took over maintainership for a number of years, but relinquished the role in 2014. The software remained unmaintained for several years, and was believed to be defunct. In 2020 May, Stephen van den Berg resumed maintenance again. The program has since seen multiple releases and bug-fixes.

Uses

The most common use case for procmail is to filter mail into different mailboxes, based on criteria such as sender

address An address is a collection of information, presented in a mostly fixed format, used to give the location of a building, apartment, or other structure or a plot of land, generally using border, political boundaries and street names as references, ...

, subject keywords, and/or

mailing list A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients. Mailing lists are often rented or sold. If rented, the renter agrees to use the mailing list only at contra ...

address. Another use is to let procmail call an external spam filter program, such as

SpamAssassin Apache SpamAssassin is a computer program used for e-mail spam filtering. It uses a variety of spam-detection techniques, including DNS and fuzzy checksum techniques, Bayesian filtering, external programs, blacklists and online databases. It ...

. This method can allow for spam to be filtered or deleted. The procmail developers have built a mailing list manager called SmartList on top of procmail. Procmail is an early example of a mail filtering tool and language. It is a

data-driven programming In computer programming, data-driven programming is a programming paradigm in which the program statements describe the data to be matched and the processing required rather than defining a sequence of steps to be taken. Standard examples of dat ...

language, similar to earlier line-oriented languages such as sed and AWK.

Operation

procmail reads mail messages given to it on

standard input In computer programming, standard streams are preconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), ...

, delivering or otherwise dispositioning each one. procmail is typically not invoked directly by the user. Rather, some other mail program will call upon procmail to deliver a message according to the user's wishes.

Message transfer agent Within the Internet email system, a message transfer agent (MTA), mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using the Simple Mail Transfer Protocol. In some contexts, the a ...

s (MTAs), such as

Sendmail Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet. A descendant of t ...

or Postfix), can be configured to use procmail to deliver all mail. A mail retrieval agent such as fetchmail can invoke procmail as needed. The companion tool ''formail'' allows procmail to be applied to mail already in a mailbox. procmail's behavior is controlled by a config file (by default, in the user's

home directory A home directory is a directory (file systems), file system directory on a multi-user operating system containing computer file, files for a given user (computing), user of the system. The specifics of the home directory (such as its name and loc ...

) containing one or more ''recipes'', read in order. Each recipe consists of a ''mode'', zero or more ''conditions'', and an ''action''. Conditions are usually extended

regular expressions A regular expression (shortened as regex or regexp), sometimes referred to as rational expression, is a sequence of character (computing), characters that specifies a pattern matching, match pattern in string (computer science), text. Usually ...

, although there are other forms. A recipe's action is taken only if all the conditions match (logical AND). If no conditions is given, the recipe is unconditional and the action always runs. The action specifies what is to be done with the message, such as deliver it to a particular mailbox, or discard it. A recipe and its action can be ''delivering'' or ''non-delivering''. Processing of a given message stops with the first delivering recipe (unless the recipe's mode flag specifies otherwise).

Example

A simple config file might look like this: MAILDIR=$HOME/mail DEFAULT=$MAILDIR/inbox :0: * ^List-Id: .* foo-announce The above routes mail from a hypothetical mailing list to a separate mailbox called , while delivering all other mail to the mailbox, both located under the directory.

Criticism

By default, procmail will "bounce" undeliverable mail back to the sender, or discard it entirely. A mistake in the config file can result in all mail being rejected or discarded. The configuration file format is sometimes regarded as cryptic. procmail is not well-suited for processing mail involving Multipurpose Internet Mail Extensions (MIME). It cannot decode or recognize MIME-specific headers or international characters. For approximately ten years, procmail was not maintained, and multiple serious security vulnerabilities were discovered in the intervening time span (since fixed).

References

External links

* — Current source code repository and distribution point * — Procmail homepage, as it appeared when it was working * {{cite web , url = http://procmail.markmail.org/ , title = Procmail Home - MarkMail - Community libraries — Searchable archives of the procmail mailing list Mail delivery agents Cross-platform software

Uses

Operation

Example

Criticism

See also

Mail architecture

Similar programs and technologies

References

Further reading

External links