[exim] Custom error message per transport

Hello Exim users,
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@???