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Sendmail, 3rd Edition by Bryan Costales

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Rules Check Header Contents

Recall that a header line declaration looks like the following:

H?flags?name:field

Here, the H begins the line and tells sendmail that a header definition follows. The ?flags? expression causes sendmail to include the header only if one of the flags is found in the selected delivery agent’s F= equate. As you saw in the previous section, beginning with V8.10, a macro name can replace the flags. The name and a colon then follow.

Beginning with V8.10, sendmail allows the name of a rule set to replace the field value. That rule set declaration can come in two forms:

Hname: $>  rule  set
Hname: $>+  rule  set don't strip comments

Both forms basically say the same thing: if sendmail finds a header name already in a message it is processing, it passes the existing header field to the rule set indicated. The + in the second form tells sendmail to leave intact (not strip) parenthesized RFC2822 comments from the passed field:

text (comments)

The $> in the earlier declaration passes just text to the rule set, while $>+ passes the unstripped text with RFC2822 comments intact.

If the rule set specified is not a legal rule set name, or if it is missing, the following error will be printed and logged:

cf file name: line number: invalid rule set name: "bad name"

If the named rule set does not exist in the configuration file, the effect is the same as if it did exist and had returned a legal value.

Rule sets called to process headers can return two possible rejection values, ...

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