There is an interesting dispute about this. The Manos Halevi explains that the mitzvah is to show friendship (the opposite of what Haman said מפוזר ומפורד). The Terumas Hadeshen says that the mitzvah is to make sure that everyone has enought food for the seuda.
The Acharonim point out a number of נ"מ based on this:
1. What if you send it to someone and they don't accept? According to teh Manos Halevi you were Yotze, you showed friendship, according to the Terumas Hadeshen you were not Yotze because the person did not get food.
2. What if you send it anonymously? Accordsing to the Manos Halevi you are not Yotze, you didn't show friendship, according to teh Terumas Hadeshen you are Yotze.