Headertrim, noheadertrim, headerkeeporder, headerread, noheaderread, innertrim, noinnertrim Channel Options

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Trimming message header lines (headertrim, noheadertrim, headerkeeporder, headerread, noheaderread, innertrim, noinnertrim)

The MTA provides per-channel facilities for trimming or removing selected message header lines from messages. This is done through a combination of a channel option and an associated header option file or two. The headertrim channel option instructs the MTA to consult a header option file associated with the channel and to trim the headers on messages queued to that destination channel accordingly, after the original message headers are processed. The noheadertrim option bypasses header trimming. noheadertrim is the default.

The innertrim channel option instructs the MTA to perform header trimming on inner message parts, i.e., embedded MESSAGE/RFC822 parts, as well. The noinnertrim channel option, which is the default, tells the MTA not to perform any headertrimming on inner message parts.

The headerread channel option instructs the MTA to consult a header option file associated with the channel and to trim the headers on messages enqueued by that source channel accordingly, before the original message headers are processed. Note that headertrim header trimming, on the other hand, is applied after the messages have been processed, and is destination channel, rather than source channel, related. The noheaderread channel option bypasses message enqueue header trimming. noheaderread is the default.

Unlike the headeromit and headerbottom options, the headertrim and headerread options may be applied to any channel whatsoever. Note, however, that stripping away vital header information from messages may cause improper MTA operation. Be extremely careful when selecting headers to remove or limit. This facility exists because there are occassional situations where selected header lines must be removed or otherwise limited. Do not merely trim header lines away because you or your users find them annoying --- those header lines are there for a reason. More often than not, the header lines that users feel are superfluous are among the most important. Before trimming or removing any header line, be sure that you understand the usage of that header line and have considered the possible implications of its removal.

Header options files for the headertrim and innertrim channel options have names of the form channel_headers.opt with channel the name of the channel with which the header option file is associated. Similarly, header options files for the headerread channel option have names of the form channel_read_headers.opt.