Sendmail Configurations

The following Sendmail configurations demonstrate the /etc/mail files necessary for sendmail to operate in various roles. The configurations suit low-volume mail sites, enable various anti-spam and security features by default, and include sample SMTP AUTH and STARTTLS settings.

To determine the version of sendmail installed on a system, run the following command. Some systems install sendmail as /usr/lib/sendmail.

$ /usr/sbin/sendmail -d0 < /dev/null | grep -i version
Version 8.13.2

Consult the INSTALL file in the tarballs below for setup instructions, or look around under the config directory to see the tarball contents. Running Sendmail 8.12 or higher is recommended due to speed and feature enhancements such as PIPELINING and MILTER.

• Domain Client 8.12 - client mail configuration: all local mail to server, no incoming mail accepted.
   
• Domain Endnode 8.12 - like client, but accepts incoming mail (presumably only from a site proxy or server system).
   
• Domain Proxy 8.12 - incoming gateway relay or backup system.
   
• Domain Server 8.12 - central mail server for a site (no shell access IMAP/POP server).

I have used these configurations on FreeBSD, Linux, Mac OS X, OpenBSD, and Solaris with various amounts of tweaking. The make(1) and m4(1) commands will need to be available on the system in question, along with the cf directory tree from the sendmail source for the version of sendmail in question (default location varies).

Notes for specific operating systems.

• Mac OS X: the Apple Developers Tools will need to be installed for the m4 command to be available.
   
• RedHat Linux: the make, m4, and sendmail-cf packages are required to build the *.cf files.

Feedback on these configurations is welcome. See also the #sendmail channel on the Freenode Internet Relay Chat (IRC) network.

Related

• Sendmail Documentation - notes on using Sendmail.
   
• Sendmail Frequently Asked Questions (FAQ).
   
• sendmail.net - documentation and articles from the Sendmail folks.
   
• comp.mail.sendmail - usenet discussion on sendmail; search it at Google Groups.
   
• Integrating Sendmail with SASL, Transport Layer Security (TLS), and PostgreSQL.

Working Domain Name System (DNS) services are essential for Internet connected systems.

• DNS Resources Directory - various documentation and links, good reference site.
   
• DNS Report - site to query and report on various DNS setup details for specified domains.

Other material.

• Design and Implementation of Highly Scalable E-Mail Systems
   
• Developing High Performance Asynchronous IO Applications
   
• A Highly Scalable Electronic Mail Service Using Open Systems

Filtering

Mail filtering tools. For more information on MILTER, visit milter.org.

• Anomy Mail Sanitizer - filter designed to block email-based security risks, such as trojans and viruses.
   
• Clam AntiVirus - open source anti-virus toolkit.
   
• demime - utility to strip MIME attachments from mailing lists.
   
• Xaminelt - Unix e-mail server scanner (previously Inflex).
   
• j-chkmail - milter filter for attachments.
   
• maildrop - mail delivery agent with filtering abilities.
   
• MailScanner - anti-virus/spam scanner.
   
• Milter Introduction & Products List
   
• MIMEDefang - flexible perl-based MILTER message handler.
   
• Procmail - mail filtering/delivery agent.
   
• Xamime - commercial mail content handler.

Various anti-malware and anti-spam resources.

• Sendmail configuration notes against malware.
   
• SpamAssassin.
   
• Stopping Spam and Trojan Horses with BSD.

Utilities

Utility scripts for mail administration. For moving messages out of queues (e.g. stuck spam delivery status notifications or viruses), either use the queuegroup feature or the qtool.pl command available the contrib directory of the Sendmail source. The 8.12.9 release of Sendmail adds _FFR_QUEUERETURN_DSN, which can shorten the time spent trying to send delivery status notifications.

• deferit.sh - script to defer mail delivery.
   
• mailreturn.sh - means to return stuck queue items immediately and gracefully.
   
• mreport
   
• rlytest - utility to test mail host for third-party relay. Alternate port support patch.
   
• runqueue.sh - to manually clear out the sm-msp queue directory.
   
• sstats - Sendmail delivery stats.
   
• SMA - Sendmail log analyser.

Requests for Comments (RFC)

Selected mail-related RFC.

• [RFC 821] - Simple Mail Transport Protocol.
   
• [RFC 1912] - Common DNS Operational and Configuration Errors. And arguments why RFC1912 is wrong.
   
• [RFC 1869] - SMTP Service Extensions.
   
• [RFC 1893] - Enhanced Mail System Status Codes.
   
• [RFC 2142] - Mailbox names for common services, roles and functions.
   
• [RFC 2487] - Secure SMTP over TLS.
   
• [RFC 2554] - Authentication for SMTP.
   
• [RFC 2821] - Simple Mail Transport Protocol.

Books

Dead tree publications of note.

• sendmail - 3rd edition “Bat” reference tome.
   
• sendmail Performance Tuning
   
• UNIX® System Administration Handbook

The author disclaims all copyrights and releases this document into the public domain.

Questions or comments about this page? Current ruminations available on my blog.

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