Reply to old ticket from another RT

Hi,

We got some new groups of requestors who use another RT maintain by other people, the plan is make them use a our RT.
We don’t need any history so on our RT configuration that would be easy. They are only one point, some requestors have the habit to answer a old ticket (so from the another RT) and just change the email address.

For some reason I not sure I understand (the Reference does’nt match) when requestor do that, the message end up in our system in the following of a existent ticket.
So let’ s say the «another RT» called RT-OLD and the new one is RT.
In the exchange with RT-OLD the Reference look like


References: <RT-Ticket-[0-9][0-9]*@RT-OLD>
X-RT-Ticket: RTOLD #1234

and the new one

References: <RT-Ticket-[0-9][0-9]*@RT>
X-RT-Ticket: RT #1234567

When a requestor send a email he going to answer a old ticket and that going to update the ticket 1234 in the RT (meaning a ticket very very old)

Is they are any way to avoid that ?
Currently I’m using a procmail to discard any email with the Reference who match the RTOLD.

But maybe they are a better way to do that.

Regards