When sendmail reads the configuration file, macros that are declared
in that file are assigned values. The configuration-file command that declares
macros begins with the letter D
. There may only
be a single macro command per line.
The form of the D
macro configuration command is:
DXtext
The symbolic name of the macro (here, X
) is a single-character
or a multicharacter name (see Section 31.4, "Macro Names"):
DX
text
single-character name X D{XXX}
text
multicharacter name XXX
This must immediately follow the D
with no intervening
space. The value that is given to the macro is the text
,
consisting of all characters beginning with the first character following
the name and including all characters up to the end of the line.
Any indented lines that follow the definition are joined to
that definition. When joined, the newline and indentation characters
are retained. Consider the following three configuration lines:
DXsometext moretext moretext tabs
These are read and joined by sendmail to form the following
text
value for the macro named X
:
sometext\n\tmoretext\n\tmoretext
The notation \n
represents a newline character, and the
notation \t
represents a tab character.
If text
is missing, the value assigned to the
macro is that of an empty string; that is, a single
byte that has a value of zero.
If both the name and the text
are missing,
the following error is printed, and that D
configuration
line is ignored:
[5]
[5] Prior to V8 sendmail, a macro whose name was missing was given arbitrary garbage as a value. This caused the sendmail program to crash.
Name required for macro/class
Table 31.2 shows the macro names that must (prior to V8.6) be given values in the configuration file.
Macro | Description | As of V8.7 | |
---|---|---|---|
$e | Section 34.8.65, SmtpGreetingMessage or $e | The SMTP greeting message | The SmtpGreetingMessage option |
$ja | Section 31.10.20 | Official canonical hostname | Automatically defined all V8 |
$l | Section 34.8.72, UnixFromLine or $l | UNIX From format | The UnixFromLine option |
$n | Section 31.10.26 | Name used for error messages | Automatically defined |
$o | Section 34.8.45, OperatorChars or $o | Delimiter operator characters | The OperatorChars option |
$q | Section 31.10.30, $q | Format of the sender's address | No longer used |
Each of these macros is described at the end of this chapter in Section 31.10. Prior to V8.7, failure to define a required macro could have resulted in unpredictable problems. Beginning with V8.7 sendmail, no macros are required. Some are predefined [6] for you by sendmail, and others have become options.
[6] But you still may need to declare an occasional macro in your configuration file to solve unusual problems.
The text
of a macro's value in the configuration
file may contain escaped control codes.
Control codes are embedded
by using a backslash escape notation. The backslash escape
notations understood by sendmail are listed in
Table 31.3.
Notation | Placed in Text |
---|---|
\b | Backspace character |
\f | Formfeed character |
\n | Newline character |
\r | Carriage-return character |
\\ | Backslash character |
All other escaped characters are taken as is.
For example, the notation \X
becomes a X
, whereas
the notation \b
is converted to a backspace
character (usually a CTRL-H).
For example,
DXO\bc May\, 1996 becomes O^Hc May, 1996
Here, the \b
is translated into a backspace (^H
)
character, and the \,
is translated into a lone comma
character.
Note that prior to V8.8, the first comma and all characters following it were stripped from the text unless the comma was quoted or escaped. For example,
DXMay, 1996 becomes May
Beginning with V8.8 sendmail, the comma is no longer special in defined macros.
Quoted text
will have the quotation marks stripped.
Only double quotation marks are recognized. Multiple parts of
text
may be quoted, or text may be quoted entirely.
Trailing spaces are automatically stripped. If you need to keep trailing spaces you need to quote them:
DX"1996 "
Leading space characters are retained in text
whether they are quoted
or not. Spaces are harmless provided that the macro
is used only in rules (because spaces are token separators); but
if the macro is used to define other macros, problems can arise.
For example,
Dw ourhost DH nlm.nih.gov Dj $w.$H
Here, the text
of the $w
and $H
macros is
used to define the $j
macro. The $j
macro is used in
the HELO SMTP command and in the Message-ID:
header
line. The value given to $j
by the above is
ourhost. nlm.nih.gov two a space spaces
Here, the value of $j
should contain a correctly formed, fully qualified
domain name. The unwanted spaces cause it to become
incorrectly formed, which can cause mail to fail.