The sendmail program was originally written by Eric Allman while he was a student and staff member at the University of California at Berkeley. At the time, one campus machine (Ingres) was connected to the ARPAnet, and was home to the INGRES project where Eric was working. Another machine (Ernie CoVax) was home to the Berkeley UNIX project and had recently started using UUCP. These machines (as well as several others on campus) were connected by a low-cost network built by Eric Schmidt, called BerkNet. Software existed to move mail within ARPAnet, within UUCP, and within BerkNet, but none yet existed to move mail between these three networks.
A sudden increase in protocol types, coupled with the anticipation of an explosion in the number of networks, motivated Eric to write delivermail - the precursor to sendmail. The delivermail program was shipped in 1979 with 4.0 and 4.1 BSD UNIX. Unfortunately, delivermail was not flexible enough to handle the changes in mail routing requirements that actually occurred. Perhaps its greatest weakness was that its configuration was compiled-in.
In 1980, ARPAnet began converting from NCP (Network Control Protocol) to TCP (Transmission Control Protocol). This change increased the number of possible hosts from 256 to over one billion. Another change converted from a "flat" host-name space (like MIT-XX) into a hierarchical name space (like XX.MIT.EDU). Prior to these changes, mail was transported using the ftp protocol (File Transfer Protocol). Afterward, a new protocol was developed for transporting mail called SMTP (Simple Mail Transfer Protocol). These developments were not instantaneous. Some networks continued to run NCP years after most others switched to TCP. SMTP itself underwent many revisions before finally settling into its present form.
Responding to these and other changes, Eric evolved delivermail into sendmail. To ensure that messages transferred between networks would obey the conventions required by those networks, Eric took a "liberal" approach - modifying address information to conform, rather than rejecting it. At the time, for example, UUCP mail often had no headers at all, so sendmail had to create them from scratch.
The first sendmail program was shipped with 4.1c BSD (the first version of Berkeley UNIX to include TCP/IP). From that first release to the present,  Eric has continued to enhance sendmail, first at UC Berkeley, then at Britton Lee, then back at UC Berkeley, and now with InReference Inc. The current version of sendmail is 8.x (or V8 for short). V8 is a major rewrite that includes many bug fixes and significant enhancements.
 With one long gap between 1982 and 1990.
But Eric wasn't the only one working on sendmail. In 1987, Lennart Lovstrand of the University of Linköping, Sweden, developed the IDA enhancements to BSD sendmail Version 5. IDA (which stands for "Institutionen för Datavetenskap") injected a number of improvements into sendmail (such as support for dbm files and separate rewriting of headers and envelopes) and fixed a number of bugs. As the '90s approached, two offspring of IDA appeared.
Neil Rickert (Northern Illinois University) and Paul Pomes (The University of Illinois) took over maintenance of IDA sendmail. With contributions from around the world, their version (UIUC IDA) represents a continuation of the work begun by Lennart Lovstrand. Neil focused on fixing and enhancing the configuration files into their current m4-based form. Paul maintained the code, continually adding enhancements and fixing bugs. In general, their version was large, ambitious, and highly portable. It succeeded in solving many complex mail routing problems.
A variation on IDA sendmail was also developed by Paul Vixie (while at Digital Equipment Corporation). Called KJS (for King James sendmail), it was a more conservative outgrowth of Lennart Lovstrand's last IDA release. The focus of KJS was on code improvement rather than changes to configuration files.
In addition to these major offshoots, many vendors have modified sendmail to suit their particular needs. Sun Microsystems made many modifications and enhancements to sendmail, including support for nis and nisplus maps. Hewlett Packard also contributed many fine enhancements including 8BITMIME support.
This explosion of sendmail versions has led to a great deal of confusion. Solutions to problems that work for one version of sendmail fail miserably with others. Beyond this, configuration files are not portable, and some features cannot be shared.
In 1994, Eric began work on V8.7 sendmail. The first major departure from tradition in years, V8.7 introduces multicharacter option and macro names, new interactive commands to use with -bt mode, and fixes many of the problems and limitations of earlier releases. But, more important, V8.7 has officially adopted most of the good features from IDA, KJS, Sun, and HP's sendmail, and kept abreast of the latest standards from the Internet Engineering Task Force. In 1996, Eric began work on V8.8 sendmail. This release continued the trend begun with V8.7, adding many requested new features and options, and tightening security. Since V8.8 is now the official release of sendmail, it is the one solely documented in this book.