sendmail, 4th Edition

H* a Default for All Headers

The preceding two sections have shown it is possible to screen specific headers for properties to accept or reject. There will be times, however, when you might wish to screen all headers that do not have their own rule sets. Using an * in place of the header name provides just such a mechanism:

H*: $>ScreenAll

The * tells sendmail to pass all headers, except those that have their own H configuration line rule set, to the ScreenAll rule set. Use $>+ instead of $>, if you want to prevent sendmail from stripping RFC2822 parenthetical comments from each header’s value.

Consider a site that sends email only to mailing lists. On such a site, it is desirable to prevent mail that is considered spam from going out. One way to do this is to reject all mail that contains addresses that are in either Cc: or Bcc: headers (good addresses should only be in To: headers). Such a site might have an mc file that contains the following:

LOCAL_CONFIG
C{BannedRecipientHeaders} Cc Bcc
H*:     $>CheckBanned

LOCAL_RULESETS
SCheckBanned
R $*                              $: $&{hdr_name}
R $={BannedRecipientHeaders}      $#error $@ 5.7.0 $: "553 Banned recipient header"

The LOCAL_CONFIG part of this mc file contains two configuration commands. The first declares a class called BannedRecipientHeaders and assigns to that class a list of header names that should be banned, those being the Cc: or Bcc: headers with the colon removed.

The second configuration command starts with the wildcard form of the H configuration command. ...