I just checked, and found that RT 1.0.7 does not put an
In-Reply-To header in the messages it sends (auto-reply, reply).
I want that enough to write the (probably trivial) patch myself
(I’m always grumbling about luser MS mudware that doesn’t put
them in), but if somebody’s already written the patch, I’ll take
it 
Is there a patch to set auto-acks for all incoming mail (such
as “You have added the following correspondence to incident
ticket xxx”)? Danger with mail loops makes this non-trivial, of
course.
#include <std_disclaim.h> Lorens Kockum