Does white-listing 'postmaster' white-list all the other recipients?

[J. Johnson]

A while back I was wondering why certain spammers kept hitting our
'postmaster' account, then i realized there were multiple recipients. It
seems like the other recipients ride in on the back of 'postmaster', then
are free to go there individual ways. Does anyone know if that is true? And
if so, how can the additional recipients be suppressed?