rewriting email headers

[Michael Fair]

If nobody's responded yet, I'd recommending
starting with the Sendmail list.

-- Michael --

----- Original Message -----
From: "Arley Carter" <arc at twinds.com>
To: <info-cyrus at andrew.cmu.edu>
Sent: Friday, September 06, 2002 3:04 PM
Subject: rewriting email headers


> I  would like to strip the headers from email originating from out NAT'ed
> network 182.168.1.0
> and replace it with the ip of the cyrus mail server that resides out on
the
> external network.  I have doing this with checkcompat in conf.c, using the
> example in Chapter 20 of the O'Reilly sendmail book.  However, I have had
no
> success here
>
> The arguments for addheader have changed in sendmail 8.12.5 since the book
> was
> writen, (8.8 I believe)  it takes 4 arguments now instead of three as in
the
> example   The correct arguments for 8.12.5  are:
> addheader(name of field, value of field, flag, envelope).  I
> Below is the code I have modified and used.
>
> /* Checkcompat subroutine from O'Reilly Sendmail v2 Chap 20 p 294. Removes
> Internal addresses from Received from header.  Makes everything appear as
it
> originates from the mail hub on the public net.  This is needed because
some
> mail servers refuse to accept mail if they can't resolve the  Received
from
> header.  */
>
> # define OUR_NET_IN_HEX 0x4152f3E0 /* external net 65.82.243.224 in hex */
> # define OUR_NETMASK 0xfffffff8   /* 255.255.255.248 */
> /* # define OUR_NET_IN_HEX 0xc0a80100 * / /* 192.168.1.0 in hex */
> /* # define OUR_NETMASK 0xffffff00 */ /* 255.255.255.0 */
> # define LOOP_CHECK "X-Loop-Check"
>
> checkcompat(to, e)
>         register ADDRESS *to;
>         register ENVELOPE *e;
> {
>         HDR *h;
>         int cnt;
>
>         if (RealHostAddr.sa.sa_family == 0)
>         {
>                 /* this is a locally submitted message */
>                 return EX_OK;
>         }
>         if (RealHostAddr.sa.sa_family != AF_INET ||
>         (RealHostAddr.sin.sin_addr.s_addr & OUR_NETMASK) !=
OUR_NET_IN_HEX)
>         {
>                 /* not received from the internal network */
>                 return EX_OK;
>         }
>         if (hvalue(LOOP_CHECK, e->e_header) != NULL)
>         {
>                 /* We've stripped them once already */
>                 return EX_OK;
>         }
>         addheader(LOOP_CHECK, "loop check", 0, &e->e_header);
>
>         for (cnt = 0, h = e->e_header; h != NULL; h = h->h_link)
>         {
>                if (strcasecmp(h->h_field, "received") != 0)
>                        continue;
>                if (cnt++ == 0)
>                        continue;
>                clrbitmap(h->h_mflags);
>                h->h_flags |= H_ACHECK;
>         }
>         return (EX_OK);
> }
>
> The use of   &e->e_header as the fourth argument to addheader generates a
> warning about passing an incompatible pointer type.
>
> The substitution that should happen, suppressing the real ip of the
sending
> machine on the internal net happens where strcasecmp find the "received"
> header and clears that field with clrbitmap.
> H_ACHECK should cause the header to be discarded.
>
> However, this isn't happening.  From is still from the internal network
> address not from the mail server address.  Message ID also reflects the
> internal network.  I believe this can be changed by setting Message Id to
> H_ACHECK on the client machine's conf.c   Another question this raises is
it
> is easy enough to do this
> on a unix baix in conf.c.  Where is this value set on a windows box?
>
> I don't see where the From field is being reset to the mail server
machine's
> ip unless sendmail should be filling this field with the mail server's ip
> automagically when it finds the blank from field we cleared out here in
> another part of the sendmail code.
>
> Can somebody clue me in where I am going off the trail here?
>
>
>