sendmail, 4th Edition

The C Class Command

The C form of the class command causes values to be assigned from within the configuration file. In general, the C class command looks like this:

CX list               ← values from configuration file
C{XX} list            ← values from configuration file

Here, list is a list of string elements (delimited by whitespace) that follows on the same line as the C command. Each word in list is added to the collection of values in the class $=X in the first case and to the class $={XX} in the second.^[331]

Multiple declarations of the same named class can coexist in the configuration file. Each declaration after the first adds its string elements to those already in the collection. That is:

CX string1 string2
CX string3 string4

produces the same collection of class strings as does:

CX string1 string2 string3 string4

Both create a class containing four strings.

Whitespace separates one value from another. Whitespace is defined by the C-language isspace(3) routine and usually includes the space, tab, newline, carriage return, and form feed characters. Each line of text assigned to a class is broken up by sendmail into whitespace-delimited words when the C configuration command is parsed.

When a line is indented with a space or a tab, that line is joined by sendmail to the preceding line. Thus, the following three declarations also add four words to the class $=X:

CX string1
CX string2
CX string3
      string4
   ↑
   tab

Words that are added to a class cannot be removed after sendmail has read them. Instead, they must ...