The IMTA provides per-channel facilities for trimming or removing selected message header lines from messages. This is done through a combination of a channel keyword and an associated header option file or two. The headertrim keyword instructs the IMTA to consult a header option file associated with the channel and to trim the headers on messages queued to the channel accordingly, after the messages are processed. The noheadertrim keyword bypasses header trimming. noheadertrim is the default.
The innertrim keyword instructs the IMTA to perform header trimming on inner message parts, for example, embedded MESSAGE/RFC822 parts. The noinnertrim keyword, which is the default, tells the IMTA not to perform any header trimming on inner message parts.
The headerread keyword instructs the IMTA to consult a header option file associated with the channel and to trim the headers on messages queued to the channel accordingly, before the messages are processed. Note that headertrim header trimming, on the other hand, is applied after the messages have been processed. The noheaderread keyword bypasses message enqueue header trimming. noheaderread is the default.
Header options files for the headertrim and innertrim keywords 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 keyword have names of the form channel_read_headers.opt. These files are stored in the IMTA configuration directory, /etc/opt/SUNWmail/imta/.