After posting a new topic a "thanks_for_posting" page is being displayed.
I like to edit that page but dunno what it is called, where it is located.

What version of UBB?

ubb 6.3
did not occure to me that their might be differences

thanks in advance

If you only want to edit the wording on that page, you can edit the "thanks_for_posting" Wordlet in the Primary Wordlet List.

And if you want to edit the look, it's sub Transition, in file public_common.pl (and the UBB version doesn't matter in this case )

Thanks LK, that was the answer I was waiting for