Guerin: in the beginning was the sendmail. and sendmail had a couple of competitors, yea, even pmdf, which sucked greatly. and pmdf was used in Dynix, and some vendor Unixes, yea, and VMS, and all right-thinking unix administrators used sendmail. And debian also used sendmail. Guerin: And lo, it came to pass that some Unix people beheld sendmail, with a complex config file and bounteous security holes, and they cried, lo, we can do better. thus there arose smail. and debian beheld smail, and saw that it was good. and debian defaulted to smail. Guerin: And it came to pass in those days that smail grew old and fat and full of holes, even as its father sendmail had done before it. And in that land there arose several Competing Implementations, and among these were qmail, exim, zmailer, and postfix. Guerin: And the fathers of Debian beheld exim, and saw that it was lovely to the eye and sweet to the config file. and qmail also was lovely, but there were some who cried, hark, qmail is non-free. and zmailer was a niche product optimized only for large queues and parallelism, and postfix was yet young. Guerin: And there arose Advocates in the debian community who spake unto the community, saying, come, let us abandon our sendmail and our smail and let us move exim into the default install. and so it came to pass. Guerin: Many years passed, and postfix matured, and zmailer faded, and sendmail shed most of its security holes, and exim evolved into exim4, and qmail continued to be non-free. Guerin: And thus today we have exim4 in the default install, yea, even the descendent of exim, and none have seen fit to change the default, as this would entail a Flame War, and exim4 is rightly perceived to be Not Too Bad.