Exim is a mail transfer agent (MTA), the program that moves email between servers on Unix-like systems. It is distributed under the GNU General Public License. Exim routes mail and checks incoming messages, and cPanel server software lists it among its mail components.
History of Exim
Creator: Philip Hazel (original author); the Exim Maintainers (later). Year: 1995.
Philip Hazel wrote the first version of Exim in 1995. He wrote it for the e-mail systems. Those systems belonged to the University of Cambridge Computing Service. The name first stood for EXperimental Internet Mailer. Exim was based on an older mail transfer agent (MTA). That agent was Smail-3. Over time, its design and approach moved away from Smail-3.
In 1997, Hazel replaced the POSIX regular expression library. Henry Spencer wrote that library. It was an older library. Hazel replaced it with a library he wrote. The new library is called Perl Compatible Regular Expressions (PCRE). It is called PCRE for short. Exim uses PCRE to match patterns. It does this in its settings and routing rules. Many other programs now use PCRE too.
Hazel retired from the University of Cambridge in 2007.1 He left his post then. A team of maintainers then took over Exim. The project still issues releases. Version 4 is the redesign. The official site lists four security notices for the 4.100.1 release. Each notice has its own GCVE identifier. The notices are listed on the site's security page.
Changelog and latest update
Exim sets mail policy in its settings. Access control lists (ACLs) let an administrator decide which hosts may send or relay mail. In version 4, ACLs became the main way to set these controls. A content scanning framework was added. Anti-virus and anti-spam tools can use it to check messages. Wikipedia says the framework let these tools be integrated.
Security history is part of the Exim changes. The official site states that all versions before 4.100.1 are out of date. The site also says the last 3.x release was 3.36 and is twenty years obsolete.
The official Exim site calls the 4.100.1 release a security release. It lists four notices that the release addresses. Each notice has its own identifier. The site also says the last 3.x release was 3.36. It says that release is twenty years out of date. The site states that maintenance releases are mainly for package maintainers. Beta versions appear in the Testing directory on the FTP sites.
Latest update: Exim 4.100.1, not confirmed
The official Exim site lists 4.100.1 as the latest version. It calls the release a security release. The release addresses four GCVE identifiers. The site states that every version before 4.100.1 is out of date. The release date was not shown on the page that was read. So the date is not confirmed. The date field is left blank in this article.
Usage examples
Exim reads its main configuration file. Then it routes each message. The commands below run on the mail server shell. They show the version. They show the mail queue. They show a routing test for one address. They show the log of one queued message. Replace the message ID and addresses with values from your server before use.
exim -bV
# Exim version 4.100.1 ...The -bV option prints the Exim version. It also prints the build options and the path to the configuration file. Use it to confirm the installed version before an upgrade. The output line is a placeholder. The real value comes from the server.
exim -bp
exim -bpcThe -bp option lists the messages waiting in the queue. It shows each one's age, size, sender and recipient. The -bpc option prints only the number of queued messages. A queue with many messages can show a delivery problem. One example is a blocked remote server.
exim -bt user@example.comThe -bt option tests how Exim routes an address. It does not send any message. The output shows the router that handles the address. It also shows the transport that delivers it. Use the test to check a new mailbox or a forwarding rule. Do this before the rule is used.
exim -Mvl 1abcDe-0000ab-CDThe -Mvl option shows the log lines for one message ID. The message ID comes from the queue listing or the mainlog file. The log lines show each delivery attempt. They show the response from the remote server. They also show any error text.
References
These sources are outside Websnoogie and were checked on 2026-10-12.
Exim
Wikipedia, Wikimedia Foundation
Encyclopedia article on Exim. It covers the 1995 origin at the University of Cambridge, the 1997 PCRE change, the 2007 maintainer transition, the security history of version 4 and the two configuration styles.
Exim Internet Mailer home
Exim project
Official home page of Exim. It states the latest version, 4.100.1, its security release status and the obsolescence of earlier versions. It also links to the download, documentation, mailing list and bug pages.
Exim documentation
Exim project
Official documentation index for Exim. It lists the main specification, the book, the wiki and the FAQs. It explains that the text documentation ships in the source archive and that PDF and texinfo forms are on the FTP sites.
Exim specification, introduction
Exim project
Chapter one of the Exim specification. It describes what Exim does as a mail transfer agent, how it routes and delivers mail, and how it differs from other mail programs. The commands in this article are described in later chapters.
RFC 5321: Simple Mail Transfer Protocol
IETF, RFC Editor
Internet standard for SMTP, the Simple Mail Transfer Protocol. Exim speaks SMTP with other mail servers when it sends and receives messages. The standard defines the commands and reply codes that appear in the delivery logs.
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