Reg. Postfix Subject line modification

Hi and How are you? At present, I have an interesting issue that I am
working on.
We are working as a team providing solutions to the govenmental
institution working on sensitive email system completely based on open
source.
One of the requirement is modification that involves adding a unique id
to the subject line.
Eg.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%
To: MyGoogleId@gmail.com
cc: Postfix_Google@gmail.com
Sub: Reg. Postfix inquiry
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%
As per the requirement the subject line should be
Sub: [12312545467] Reg. Postfix inquiry
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%
The unique ID need to be added to the subject line after the user send
an email to an individual user or the group.

I appreciate for your time and effort spent on this email and thank you
in advance for your responses.
-Saravanan Kannan