What will happen if I write incomplete address on a postal item and send it?

Question

I sent my friend a book as a birthday present. 
But after I sent the book, I noticed that I needed to write the room number and building number of my friend. I did not know that my friend lived in an apartment. So I just wrote the name of city, street number, state, and zip code. Can the post office send my book to my friend without his room number and building number? Or if they can not, do they return the book to me?
Since this present is surprise, I can not ask him about the address.
Also none of my friends knows his address.

I sent the book by USPS. It was a priority mail.

Answer

It most likely will be returned, but if it were sent by U.S. mail there is the chance that the local carrier might be accustomed to his name and address & apt. #.

Answer

There was instances that when the address was not complete they returned back the mail to the sender but if the carrier or postman was familiar with the place even there were no building number and room number it will be delivered to the receiver.

What will happen if I write incomplete address on a postal item and send it?

Answers (2)