List Fails to Add Certain Header Fields
Why are some of my mgrpAddHeader or mgrpRemoveHeader attribute values ignored?
The MTA maintains a list of well over 500 "known" header fields. The MTA's header trimming facilities are built on top of this list and only fields on this list can be manipulated using header trimming. This is in contrast to the MTA's header addition facilities, which can add arbitrary header fields to messages. (Also see the Sieve editheader extension which permits manipulation of arbitrary, including unknown-to-the-MTA, header fields.)
Support for both the
mgrpRemoveHeader group attributes is built on top of the header trimming facility, not the header addition facility. This means that these attributes can respectively only add or remove fields on the MTA's internal list. In practice this should not be a major issue since the list is so large.
Prior to the 6.3 release of Messaging Server the MTA might have attemped to add or remove a field that wasn't on the list. Unfortunately doing this could cause various problems, including but not limited to removing other unrelated fields or adding fields without properly formated field name. As of 6.3 the MTA silently ignores requests to add or remove unknown fields.
See Header Fields Known to the MTA for a copy of the list.
The header list is compiled into the MTA so updating, while a straightforward matter of editing a file, requires recompilation and generation of new binaries. Justifiable requests to add headers to the list can be made to Oracle and will probably be honored but there will necessarily be some delay before binaries supporting the addition can possibly be made available.