Header option files
Some special option files may be associated with a channel that describe how to trim the headers on messages either enqueued to, or enqueued by, that channel. This facility is completely general and may be applied to any channel; it is controlled by the
noheaderread channel options.
Various MTA channels have their own channel-level option files as well. Header option files have a different format than other MTA option files and thus a header option file is always a separate file.
Note that the
test -header utility with its
-option switch can be used to test the effects of header trimming option files.
As of MS 6.3, note that the Sieve "
editheader" extension provides an alternate way to alter header lines. While header trimming may be a simpler approach for performing simple changes, the Sieve "
editheader" approach is more powerful in some respects such as allowing changes to specific, unrecognized-by-the-MTA, header lines, or alterations of the values on header lines.