[exim] no @ found in the subject of an address list match

That's something that has been happeining on and off in my panic log. The
error messages I get there are of the form:

no @ found in the subject of an address list match: subject="mailer-daemon"
> pattern="do-not-reply@localhost"
>

I finally took the time yesterday to try to figure it out. I have a router
that reacts to the local parts starting from "support" and "do-not-reply" to
do special bounce processing.

support_local:
local_part_prefix = support-:do-not-reply-
caseful_local_part
driver = accept
transport = support_delivery
no_verify

It appears that if I get a bounce from a certain external host running a
barracuda, that host doesn't include the domain name after "mailer-daemon"
in its bounces, which makes Exim complain. Here's the relevant part from the
Exim source code:

/* The only case where a subject may not have a domain is if the subject is
> empty. Otherwise, a subject with no domain is a serious configuration error. */
>

> if (sdomain == NULL && *subject != 0)
>   {
>   log_write(0, LOG_MAIN|LOG_PANIC, "no @ found in the subject of an "
>     "address list match: subject=\"%s\" pattern=\"%s\"", subject, pattern);
>   return FAIL;
>   }

>
>
Is there a way to handle it better? I.e., is there a way to handle a
situation where there is no domain part on an incoming, external, message?

Thanks!
Sergei