On Wed, 26 Jan 2005, Jeremy Harris wrote:
> Version 4.43
>
> I'm setting up headers_add in router "A", doing an unseen delivery in router
> "B" then a real delivery in router "C". The real delivery
> doesn't seem to get the headers added. Is this expected?
Yes. The documentation says it, but the current edition is not very
clear. It says:
Exim does not check the syntax of these added header lines. If an address
passes through several routers as a result of aliasing or forwarding
operations, any "headers_add" or "headers_remove" specifications are cumu-
lative. This does not apply for multiple routers that result from the use
of 'unseen'.
As it happens, I have in fact already re-written the documentation about
header modifications for the next edition.
What happens when a router does the "unseen" thing is that the original
address becomes a "parent" with two children, the unseen delivery one,
and a new clone that is passed to the next router (like an alias with
two children). The delivered address gets all the header modifications
so far specified - from previous routers and from the "unseen" router
itself. The new clone gets none.
This setup allows you to add headers to an address until it is "unseen"
delivered; the subsequent routers then start again with an empty slate.
In the code, there is this comment:
/* As it has turned out, we haven't set headers_add or headers_remove for the
* clone. Thinking about it, it isn't entirely clear whether they should be
* copied from the original parent, like errors_address, or taken from the
* unseen router, like address_data and the flags. Until somebody brings this
* up, I propose to leave the code as it is.
*/
I think the current facility is probably useful to some people, and I
don't think that making an incompatible change is a good idea. I suppose
this means that, if copying the headers from router "A" and its
ancestors is wanted, an option will be needed. I presume that copying
header_{add,remove} settings from router "C" is NOT wanted. Or are they?
Maybe it should be all or nothing?
--
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
Get the Exim 4 book: http://www.uit.co.uk/exim-book
