Postcrossing - Help
Can I specify which cards I want to receive?
No. However, you may say what your preferences are in your profile. What you write will indicate to other members what type of postcards you like to receive; however, it does not necessarily guarantee that they can or will fulfil your preferences.
You must still register all postcards you receive regardless of whether they match your preferences or not. Therefore, stating in your profile that you will not register X or Y type of postcards is against the rules.
Remember that Postcrossing is not a collector's website - it is a postcard exchange website.