sendmail, 4th Edition

Reply Versus Bounce

The eventual recipient of a mailing-list message should be able to reply to the message and have that reply go to either the original sender or the list as a whole. Which of these happens is an administrative decision. In general, replies go to the address listed in the From: or Reply-To: header. If the intention is to have replies go to the list as a whole, these headers need to be rewritten by a filter at the originating site:

list:   "|/etc/local/mailfilter list -oi -odq -flist-request list-real"

Here, the name of the filter has replaced sendmail in the aliases file entry. Writing such a filter is complex. The original addresses need to be preserved with appropriate headers before they are rewritten by the filter.

The converse problem is that not all mail-handling programs handle replies properly. Some programs, such as UUCP and certain versions of emacs-mail, insist on replying to the envelope sender as conveyed in the five-character "From" header. By setting up lists correctly (as we showed earlier), an administrator can at least guarantee that those replies are sent to the list maintainer, who can then forward them as required.

A more serious problem is the way other sites handle bounced mail. In an ideal world, all sites would correctly bounce mail to the envelope sender and (less desirably) to the Errors-To: address, which, beginning with V8.8, is supported only if the UseErrorsTo option (UseErrorsTo on page 1115) is set to true.^[212] Unfortunately, not all ...