[exim] Logging particular header | returning message ID

Hello,

I need to find a way to identify emails that exim handles with messages
the mailing system produced. The purpose is mostly to be able to trace
the fate of an email on click.

For that I need either the exim process to return the message ID (if it
is called with the /usr/bin/sendmail method) or I need exim to log one
particular header of the mail that contains the platforms internal
message ID.

While both would work logging the message ID (of the sending program)
would make it easier...

Does anyone have an idea how that can be done?

Greetings
Björn