MIMEDefang is a

GPL The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general us ...

licensed A license (or licence) is an official permission or permit to do, use, or own something (as well as the document of that permission or permit). A license is granted by a party (licensor) to another party (licensee) as an element of an agreeme ...

framework for

filtering Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component th ...

e-mail Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" mean ...

. It uses

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 the ...

's "

Milter Milter (portmanteau for ''mail filter'') is an extension to the widely used open source mail transfer agents (MTA) Sendmail and Postfix. It allows administrators to add mail filters for filtering spam or viruses in the mail-processing chain. ...

" API, some C

glue code Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

, and some Perl code to let the user write high-performance mail filters in

Perl Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...

. MIMEDefang can be used to: * Block

viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room ...

(e.g. using

Clamav Clam AntiVirus (ClamAV) is a free software, cross-platform antimalware toolkit able to detect many types of malware, including viruses. It was developed for Unix and has third party versions available for AIX, BSD, HP-UX, Linux, macOS, OpenVMS, ...

) * Block or tag spam (e.g. using

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 is ...

) * Remove

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScri ...

mail parts * Add boilerplate disclaimers to outgoing mail * Remove or alter attachments * Replace attachments with URLs * Implement sophisticated

access control In the fields of physical security and information security, access control (AC) is the selective restriction of access to a place or other resource, while access management describes the process. The act of ''accessing'' may mean consuming ...

s * Verify and add DKIM and ARC signatures

History

MIMEDefang was originally developed by Dianne Skoll, who was contracted by the

Royal College of Physicians and Surgeons of Canada The Royal College of Physicians and Surgeons of Canada (french: Collège royal des médecins et chirurgiens du Canada) is a regulatory college which acts as a national, nonprofit organization established in 1929 by a special Act of Parliament to o ...

in 2000 to help stop the flood of email viruses to the college's

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

. The software was written to filter attachments and was originally called MIMESweeper, then MIMEDefanger, and currently MIMEDefang. Skoll announced her software to the public on August 28, 2000. On December 21, 2001, a version incorporating support for

was released, making MIMEDefang a filter for both spam and viruses. Skoll's company, Roaring Penguin Software, developed and sold a commercial anti-spam product known as CanIt, which is based on the open-source version of MIMEDefang. Roaring Penguin Software was acquired by AppRiver in March 2018. On March 5th, 2020, AppRiver agreed to give The McGrail Foundation leadership of the open-source MIMEDefang project for a period of three years, automatically renewable for one-year terms after that unless either AppRiver or The McGrail Foundation chooses not to renew the agreement. On May 28th, 2021, Dianne Skoll announced a fork of the project, known as Mailmunge.

Architecture

The

library included with Sendmail uses

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming inte ...

thread Thread may refer to: Objects * Thread (yarn), a kind of thin yarn used for sewing ** Thread (unit of measurement), a cotton yarn measure * Screw thread, a helical ridge on a cylindrical fastener Arts and entertainment * ''Thread'' (film), 2016 ...

s to allow multiple concurrent filters. MIMEDefang's Perl filter uses a pre-forked process model, similar to the traditional Apache Web server multi-processing model. MIMEDefang therefore consists of three components: * A multithreaded C program that communicates with Sendmail and the filtering processes * A

multiplexer In electronics, a multiplexer (or mux; spelled sometimes as multiplexor), also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The sel ...

(written in C) that manages a pool of Perl scanning processes (called "slaves") * A Perl program called mimedefang.pl that provides the basic filtering infrastructure. MIMEDefang users code their filtering policies in Perl, using the infrastructure provided by mimedefang.pl. They don't need to worry about thread synchronizations because each Perl filter is a separate single-threaded process. The infrastructure provided by mimedefang.pl follows the Milter API reasonably closely, but not exactly. It includes convenience routines for parsing and rebuilding MIME messages so that filter authors can concentrate on high-level policy rather than worry about low-level API details. This convenience comes with a small loss of flexibility and some loss of performance.

References

External links

* {{official website, https://mimedefang.org/ Free email software Spam filtering