Especially in spoken German, "der, die, das" (and all their forms, therefore also "denen") are often used as demonstrative pronouns - sometimes to lend emphasis, sometimes to make it sound a little disparaging, sometimes to avoid confusion/differentiate between "Ihnen" and "ihnen". "Soll ich den Brief an X und Y schicken?" - "Schick' ihn lieber an A und B." - "Okay, dann schicke ich ihn denen." (here, "denen" is used to make it clear that the speaker means to send the letter to those last mentioned, i.e. A and B. IMO "ihnen" would not serve the same purpose. Also, it serves to avoid the awkward "ihn ihnen".)