The Gemara explains that a person can be Mevatel a Shali'ach to divorce a woman since "Asi Dibur u'Mevatel Dibur." Giving a Get to the Shali'ach is not called a Ma'aseh, since the woman is not yet divorced.
How do we reconcile this with what the Rishonim write with regard to Mili Lo Memseran l'Shali'ach. The Rishonim explain that a Shali'ach can give a Get to another Shali'ach, and it is not considered Mili, since giving over the Get to a Shali'ach is considered a Ma'aseh, and not just Mili. One reason they give is because the Shali'ach can divorce her against her will, so it is as if she is already divorced (Mordechai Kidushin 41b, #505, citing "the Kadosh of Troy".
There must be some difference between the laws of Mili and the laws of
Dibur Mevatel Dibur, but I can't figure out what it is. Can you help me?
Avrohom Feldman
Whether Dibur can be Mevatel Dibur is dependent on the strength of what has taken place . If what was done is considered more than a Dibur, then in a sense the Chalos is in place and cannot be uprooted by another Dibur. If it is merely a Dibur, it can be uprooted by another Dibur. Giving a Get to a Shali'ach is merely considered Dibur, with regard to what has already taken place.
Mili deals with the ability of a person to appoint a Shaliach. Ostensibly, only the Ba'al ha'Davar should be able to make a Shaliach, since ultimately the Ma'aseh is being done for him. However, when the Shaliach has been entrusted with something which is more than Mili, he has been empowered to perform that Ma'aseh himself and therefore he is enough of a Ba'al Davar to make a Shaliach. (It is not necessary for the Ma'aseh to have actually taken place, as long as the Shali'ach has been entrusted with something that makes him a "Ba'al Davar.")
D. Zupnik
What still must be clarified is as follows. So it's true that no "partial Gerushin" has taken place when the Get is given to a Shali'ach; all that is accomplished is the appointment of a Shali'ach. But let that appointment be considered a Ma'aseh, and not just a Dibur, since it is a strong enough act to make the Shali'ach be like the Ba'al Davar. Dibur should not be able to be Mevatel such an act, since the appointment of this Shali'ach is more than Mili.
The answer to this is that no matter how strong the Shelichus is, it is always Dibur, since the definition of Ma'aseh (as far as Bitulo) is that something has been accomplished, and Minuy Shelichus only gives the potential to accomplish. The fact that it is not Mili does not mean that it is a Ma'aseh; it only means that he is the Ba'al Davar. But I couldn't convince him; maybe you can explain this point (of why making a Shali'ach is not an "accomplished Ma'aseh") more clearly.
-Mordecai Kornfeld