Some users get one email multiple times... or: how to aggregate email-adresses?

Hi,

I have some users that want to have every bit of information via email,
so they set themselves as watchers to some queues, and maybe another
user sets them as cc or admincc to a ticket he creates.

This results in some users getting the same email twice or more often.

Is there a way to prevent this? Maybe some sort of parsing the
email-address list for a single message to have only unique addresses?

Educating this special type of users is very difficult, btw. I know
most of these double emails are some sort of mis-understanding the
system ;-).

We are using RT 3.6.3.

Thank you for your help,

Stefan