You have the issue, that your agents are not cleanly reading the full e-mail on reply and sensitive data is getting therefore send by your company to arbitrary persons?
You want to ensure that only the message entered by the current agent is getting sent and that this agent has selectively choose what to send out?
In this case you need to modify your reply template to disable the quote of older messages on Reply / Reply All
How to disable quoting of previous messages
Go to Admin > System Configuration and search for
Ticket::Frontend::ResponseFormat
You see something like this:
[% Data.Salutation | html %]
[% Data.StdResponse | html %]
[% Data.Signature | html %]
[% Data.CreateTime | Localize("TimeShort") %] - [% Data.OrigFromName | html %] [% Translate("wrote") | html %]:
[% Data.Body | html %]
you simply remove the last line (Data.Body) and change it to something like this (or what suites to you needs):
[% Data.Salutation | html %]
[% Data.StdResponse | html %]
[% Data.Signature | html %]
Reply to E-Mail on [% Data.CreateTime | Localize("TimeShort") %] - [% Data.OrigFromName | html %] [% Translate("wrote") | html %]:
Test
Go to a ticket and click on Reply or Reply All
Now you shall not see the previous E-Mails as quoted text in your new compose window anymore