Save raw value from select list

CF7 has a function to send a different value to what’s in a select list.

https://contactform7.com/selectable-recipient-with-pipes/

You have a filter

apply_filters('vsz_cf7_posted_data', $contact_form->posted_data);

but it’s not clear what to do with that to save the raw value. In emails you just add _fieldname. Can you give an example?