Re: [exim-dev] SMTP transport bounce message handling

On Wed, Jul 21, 2010 at 12:35 PM, Brent Jones <brent@???> wrote:
> Hello Exim s/users/devs/g,
>
> I posted this to the exim-users list, but after reading some of the
> transports/smtp.c code, it seems like I may need the assistance from a
> developer.
>
> My original question is below, but I will expand on what I am looking
> to accomplish.
> Essentially, we have a requirement to deliver to a non-defined list of
> servers strictly through TLS. When I say non-defined, the requirement
> is user driven.
> Based on headers, subject, or arbitrary data, we have a router that
> will pass the message onto a special transport to require TLS delivery
> for the message.
> That in itself isn't a problem. But when looking at error handling, we
> would prefer an instant fail if the recipient server cannot perform
> TLS connections.
>
> Currently, the code will defer the message, which is normally fine,
> but not for our requirement.
> I found in transports/smtp.c:
>
>  #ifdef SUPPORT_TLS
>  TLS_FAILED:
>  code = '4';
>  #endif
>
> We have since added a new handler:
>
>  #ifdef SUPPORT_TLS
>  TLSREQ_FAILED:
>  code = '5';
>  #endif
>
> However, that failure doesn't generate a very descriptive bounce. It
> seems Exim normally include the response of the server as part of a
> 5xx bounce message, but since the host doesn't advertise TLS, the
> transport currently just fails the message with no additional data for
> the user to determine why it failed.
> I am trying to find a way to add additional data to the bounce. The
> log files get descriptive failure information, from this section:
>
>  save_errno = ERRNO_TLSREQUIRED;
>  message = string_sprintf("a TLS session is required for %s [%s], but %s",
>    host->name, host->address,
>    tls_offered? "an attempt to start TLS failed" :
>                 "the server did not offer TLS support");
>  pass = string_sprintf("a TLS session is required for %s [%s], but %s",
>    host->name, host->address,
>    tls_offered? "an attempt to start TLS failed" :
>                 "the server did not offer TLS support");
>
>  goto TLSREQ_FAILED;
>
> But that message does not get included with the bounce, which I would
> like it to be included.
>
> Would there be a way to pass that information to the bounce message?
>
>
> -----
> Original question:
>
> I was wondering if is possible to reference a custom error message for
> a transport.
> I would like certain transports to be more descriptive as to why a
> message was delayed, such as a transport that requires TLS. If the
> sending server doesn't offer TLS, I would like to inform the user of
> the nature of the warning or permanent error.
>
> I looked at deliver.c, but notice only two blocks for generating
> errors and warnings, which appear to be global.
>
> Any thoughts?
>
> --
> Brent Jones
> brent@???
>

I think I have found what I'm looking for actually, to a degree at least.

Line 855 of transports/smtp.c:
BOOL pass_message = FALSE;

When set to TRUE, I get the error message that is presented internally
to Exim appended to the bounce message.

I'm party way there now!

--
Brent Jones
brent@???