sendmail, 4th Edition

Trade-offs

As has been noted, the aliases file should be writable only by root for security reasons. Therefore, ordinary users, such as nonprivileged department heads, cannot use the aliases file to create and manage mailing lists. Fortunately, :include: files allow ordinary users (or groups of users) to maintain mailing lists. This offloads a great deal of work from the system administrator, who would otherwise have to manage these lists, and gives users a sense of participation in the system.

In some circumstances, reading :include: lists can be slower than reading entries from an aliases database. At busy sites or sites with numerous mail messages addressed to mailing lists, this difference in speed can become significant. Note that the -bv command-line switch (-bv on page 237) can be used with sendmail to time and contrast the two different forms of lists. On the other hand, rebuilding the aliases(5) database can sometimes be very slow. In such instances, the :include: file can be faster because it doesn’t require a rebuild each time it changes.

One possible common disadvantage to all types of mailing lists is that they are visible to the outside world. This means that anyone in the world can send mail to a local list that is intended for internal use. Many lists are intended for both internal and external use. One such list might be one for discussion of the O’Reilly Nutshell Handbooks, called, say, [e-mail]. Anyone inside oreilly.com and anyone in the outside world can ...