[Plugin: Contact Form 7] [contact form 7] checkbox values in mail separated by commas, how to change

Hello,

I have a question about the checkbox value items that I receive in my mail after someone fills in my form.

If someone has checked these three boxes in the form:
Avontuurlijk
City games
Concerten

Then in my mail they appear as:

Avontuurlijk, City games, Concerten

However I would like to change the comma separation into something else.

Either:

[Avontuurlijk] [City games] [Concerten]

or:

-Avontuurlijk- -City games- -Concerten-

I really need this, can somebody please tell me where I can change this?

Thanks already!

Marten