Chapter 13. Mailing Lists and ~/.forward

As was shown in the previous chapter, the sendmail program is able to obtain its list of recipients from the aliases file. It can also obtain lists of recipients from external files. In this chapter we will examine the two forms that those external files take: the :include: form (accessed from the aliases file) and the individual user's ~/.forward file. Because the chief use of the :include: form of alias is to create mailing lists, we will first discuss mailing lists in general, then their creation and management, and then the user's ~/.forward file.

A mailing list is the name of a single recipient^[1] that, when expanded by sendmail aliasing, becomes a list of many recipients. Mailing lists can be internal (in which all recipients are listed in the aliases file), external (in which all recipients are listed in external files), or a combination of the two. The list of recipients that forms a mailing list can include users, programs, and files.

^[1] RFC defines a mailing list as a pseudo-user's address that expands to multiple real email addresses. As you will see when we cover the ~/.forward file, real email addresses also can expand to mailing lists.