Over on the O’Reilly site, Ken Simpson and Stas Bekman write of their adventures “Fingerprinting the World’s Mail Servers.” They report:
Of the 400,000 domains we surveyed, 31.2 percent of them (still) receive their email via open source mail server software. Of these, the most popular by far is still the old guard, Sendmail (12.3 percent), with Postfix a relatively close second (8.6 percent). Exim and qmail are roughly tied (5.3 and 5.0 percent, respectively) in third place.
Interesting.