Who is MajorDomo and why do Web email lists use this expression?
MajorDomo is, in the context of the web, a Perl-based software package used to manage mailing lists.
[MajorDomo FAQ] - note: you may need to use the cached Google copy, as this link does not appear reliable.
In more general terms, a major domo is a butler, usually a senior butler in a household with a large staff. Another meaning that relates to the web usage is “one who makes arrangements or directs affairs for another”.