A majordomo is the head (major) person of a domestic staff (domo), one who acts on behalf of a usually absent owner of a typically large residence. Similar terms include castellan, seneschal, and steward. The etymology is from mayordomo (Spanish) and major domus (Latin).

See Mayor of the Palace for medieval title and office.

Majordomo is also an open source mailing list manager (MLM) developed by Great Circle Associates. It works in conjunction with sendmail on UNIX and related operating systems. It came into widespread use beginning in 1992, predating the popularity of the web browser, in an era when many people had email access but no Internet connection. As a result, tasks such as subscribing and unsubscribing are handled by sending mail messages, a process that seems cumbersome today.

There are front-ends, such as MajorCool, to provide a web interface. Many mailing lists are still run using majordomo.

Most, however, moved to commercial mailing list hosting services, often with a stipend of $100 or more paid to the list owner by the hosting service in exchange for the transfer. Most of the hosting providers were subsequently bought out by Yahoo!, and merged into its Yahoo! Groups service.

Before Majordomo, mailing lists were maintained manually, with a list owner adding and removing participants by editing a text file.

A commercial product used during the same era is Listserv.