sendmail, 4th Edition

The aliases(5) File

The aliases(5) file is one of several sources that can supply system mail aliases. We describe it first because it is the most traditional and because it illustrates the syntax and limitations common to all techniques.

The aliases(5) file is composed of lines of text. Any line that begins with a # is a comment and is ignored. Empty lines (those that contain only a newline character) are also ignored. Any line that begins with a space or a tab is joined (appended) to the line above it. All other lines of text are viewed as alias lines. The format for an alias line is:

local: alias

The local must begin a line. It is an address in the form of a local recipient address (we will discuss this in more detail soon). The colon follows the local on the same line and can be preceded with spaces or tabs. If the colon is missing, sendmail prints and syslog(3)s the following error message, and skips that alias line:

missing colon

The alias (to the right of the colon) is one or more addresses on the same line. Indented continuation lines are permitted. Each address should be separated from the next by a comma and optional space characters. A typical alias looks like this:

root: jim, sysadmin@server,
      gunther
↑
  indenting whitespace

Here, root is the local address to be aliased. When mail is to be locally delivered to root, it is looked up in the aliases(5) file. If found, root is replaced with the three addresses shown earlier, and mail is instead delivered to those other three addresses. ...