kind regards from a new user on this board.
Of cause the reason why i´m joining is a problem

We are using OTRS 2.4.7 to communicate with our customers.
A few weeks ago an employee has updated a Ticket with the status "E-mail to internal".
Another employe has answered this e-mail via Outlook with the ticketnumber in the subject.
The answer he send is now marked with the status "e-mail to extern".
The Problem is now, that our customer gots informations that are determined to internal traffic.
In other processes with the same procedure the "answer e-mail" from Outlook is marked as "e-mail to internal"
What can be the reason why this special answer goes to our customer? (e-mail to extern)
We are now afraid, that this can happen again.
Kind regards,
Chris