When I receive forwarded mail, it can come in two forms: a block of
text appearing in the contents window, displaying the entire thread
from originator to forwarder (this is often raw text, and includes
header information); or, sometimes, an icon in the initial message
which, when launched, brings up the original message as it looked to
the forwarder before s/he passed it on..
I wonder if people are receiving an embedded message and replying to
that - if so, the reply could well go directly to the originator and
not to you at all.
Worst case scenario - if in doubt, maybe have the users reply to the
message by just highlighting the message in their Outlook window,
rather than opening the message and hitting the Reply button from
inside it...
Another (extremely remote) possibility is that you've been granted Send
As permission to the mailbox of the message's originator. If you
forward a message in this fashion, and have the originator's name in
the "From:" field of the message, the person you forwarded it to would
receive it as if it came from the originator. Any replies would go
directly back to them. As I say, this is extremely unlikely, but it's
possible.
Cheers,
DW