sendmail, 4th Edition

Use $>+ to Include RFC2822 Comments

Some headers contain addresses, along with other important information, that appears as RFC2822 commentary. The Received: header is one such header:

                         RFC2822 commentary starts here
                     and ends here
                                  ↓                                    ↓
 Received: from some.other.domain ([e-mail] [29.22.14.17])
         by your.domain (8.12.4/8.12.4) with ESMTP id g5CMW6KF010979
         for <[e-mail]>; Wed, 12 Jun 2002 16:32:09 −0600 (MDT)

Other headers, such as the Subject: header, do not contain addresses:

Subject: Make money now (Adult Triple-X web site)

When screening such headers, it is important that they are not interpreted as addresses or information might be lost.

Consider the previous Subject: header’s value. If such a header were screened with an H configuration file line like this:

HSubject: $>ScreenSubject

the rule set named ScreenSubject would be given the following value to parse:

Make money now

Beginning with V8.10, sendmail offers the $>+ operator to prevent parenthetical RFC2822 comments from being stripped out of headers that do not contain addresses as values:

HSubject: $>+ScreenSubject
            ↑
          note

By using this new operator, the original subject is passed to the ScreenSubject rule set in a form that is much more intact:

Make money now(Adult Triple-X web site)

Note that because of the way sendmail splits up addresses and pastes them back together, the space between the now and the ( has been lost. But this does not matter because of the way rule matching operates.

As a side benefit, the ${currHeader} ...