Gemara

66b (R. Yirmeyah bar Aba) Question: If a man asked two to write and give a Get to his wife, and they asked a scribe to write it, and they signed it, what is the law?

Answer (Shmuel): If she remarried relying on this Get, she must leave her new husband. This law requires investigation.

Even though Shmuel said that the Halachah follows R. Yosi, who says that Mili (a mission in which the Shali'ach did not receive anything needed for the mission, or that depends on the consent of someone else) Lo Mimseran l'Shali'ach (cannot be transferred to another Shali'ach). Shmuel was unsure if the husband meant that they must sign it, or that they must write the Get itself.

Question: Shmuel holds that if 'write' means to sign, they can ask another to write the Get. Shmuel rules like R. Yosi, that Mili Lo Mimseran l'Shali'ach!

Answer: If 'write' means to sign, it is as if he told them to appoint a scribe to write it. R. Yosi agrees that Omer Imru (telling someone to appoint a Shali'ach) works.'

Question (Mishnah): A Get written by a scribe and signed by one witness is valid.

(R. Yirmeyah): The text of the Mishnah says 'Chasam Sofer (a Get signed by the scribe) and one witness is valid.'

(Rav Chisda): The Tana is R. Yosi, who says that Mili Lo Mimseran l'Shali'ach.

If R. Yosi agrees that Omer Imru works, disaster may result! If one told two people to ask a scribe to write a Get, and to ask two others to sign it, they might ask the scribe to be a witness and sign, lest he be shamed (that he was not asked to sign). The husband did not authorize this (the Get is Pasul)!

Answer: L'Chatchilah, one may not ask two people to ask a scribe and witnesses to write and sign the Get, therefore we are not concerned for the above case.

Some permit this l'Chatchilah. They must say that R. Yosi holds that Mili cannot be transferred, even regarding Omer Imru. Shmuel disagrees about Omer Imru.

71b (Mishnah): If a man authorized a Get, and they appointed a scribe to write it and witnesses to sign it, it is Batel, unless he personally told the scribe to write and the witnesses to sign.

72a (Rav Ashi): The Mishnah is like R. Yosi. It is Batel even when he said 'give', even when he told three people, and even in a case of Omer Imru.

Rishonim

Rif and Rosh (32b and 7:19): The Halachah follows R. Yosi, that Mili Lo Mimseran l'Shali'ach. Even if one explicitly asked three to ask others to write and sign a Get and give it, it is Batel.

Ran (DH v'Afilu): Shmuel holds that Omer Imru works, but the Rif learns from 66b, which says that the Mishnah allows Chasam Sofer, for Omer Imru does not work. BaHaG and R. Chananel agree. Sefer ha'Terumos rejects this proof. The Sugya did not rule like R. Yosi. Rav Ashi merely established the Mishnah like him. Even Shmuel agrees! No Amora explicitly argues with Shmuel. However, Tana'im argue about Omer Imru in a Mishnah (66b), and a later Mishnah (88a) is Stam (like R. Yosi), so we follow the Stam Mishnah.

Rebuttal (Gra EH 120:14): Amora'im may rule against a Stam Mishnah (even if Tana'im argue in a previous Mishnah. Perhaps we follow Shmuel!)

Ramban (cited in Ran DH v'Hiksheh): Why do some disqualify Omer Imru, even if he specified whom to appoint? R. Yosi requires hearing from the husband himself! Omer Imru is not Mili. One may make a Shali'ach in the Shali'ach's absence! Rather, a Get is Lishmah only if the scribe and witnesses heard the husband's command. Therefore, a woman can appoint a particular Shali'ach overseas to receive her Get. However, a Shali'ach Kabalah cannot make another Shali'ach, for this is Mili. A gift is like a Get regarding Mili, but there is no reason why Omer Imru would not help for a gift.

Rebuttal (Ro'oh, cited in Ran ibid.): If R. Yosi disqualifies even when he specified whom to appoint, what is the source that his reason is due to Mili? Perhaps it is due to Lishmah! Rather, R. Yosi disqualifies telling Sheluchim to appoint a Shali'ach only when the Meshale'ach does not specify whom to appoint. There is no concern for disaster, for Sheluchim are concerned for shaming the scribe only when they themselves decide whom to pick.

Ran: There is concern even when the witnesses themselves were asked to sign. Rather, if R. Yosi held that Mili Lo Mimseran l'Shali'ach, hearing from the Shali'ach would be like hearing from the husband, and it would be Lishmah. I agree that R. Yosi allows Omer Imru when one specifies the scribe and witnesses. We are not concerned lest witnesses intentionally appoint the wrong person, which will lead to a Pasul Get and Mamzerim, to avoid shaming the scribe. Rather, whenever witnesses are told 'tell...', they think that they may choose whom they want. If the Meshale'ach specified witnesses, they think that it is a mere suggestion; if not, he himself would have appointed them! Since R. Yosi allows only when the husband appointed, there is no concern lest the witnesses deviate.

Rambam (Hilchos Gerushin 2:6): If one asked two or three people to tell a scribe to write a Get and witnesses to sign it, and they did so, or if he asked two to tell a scribe to write a Get and they should sign it, it is Pasul (mid'Rabanan). One must ponder this matter greatly. It is very possible that the Get is Batel (mid'Oraisa).

Ra'avad: Our Gemara (71b) says that it is Batel.

Kesef Mishneh: Maharam Alashkar (21) says that the Rambam alludes to pondering if the Get is Kosher. This is difficult. Rather, it is surely Pasul mid'Rabanan, and possibly Pasul mid'Oraisa, like the Radach explains. We tell her new husband that he should be stringent, even if they have children.

Kesef Mishneh: We disqualify Omer Imru lest one allow Mili even when it is not Omer Imru. The Rambam is unsure if it is totally Batel, for the Gemara said that it is Batel if the scribe and witnesses did not hear the husband.

Rebuttal (R. Akiva Eiger): If even R. Yosi disqualifies Omer Imru only mid'Rabanan, what is the source that Shmuel disagrees? Perhaps he agrees, and was unsure if the husband was insistent that the ones he told write by themselves, and the Get is totally Batel! Rather, the Gemara deduced that if Omer Imru were Pasul, the scribe could be a witness without concern (for no one may sign without hearing from the husband). If Shmuel held like this, surely he would assume that the husband wanted them to write and sign, which is a Kosher Get, and not Omer Imru, which is Pasul! Since Shmuel was unsure what the husband intended, surely is Machshir Omer Imru.

Rosh (20): The Shali'ach must hear from the husband only for writing a Get. If it were beneficial for a woman to be divorced, one could receive a Get on her behalf without any appointment (Gitin 11b). It seems that the same applies to a Shali'ach to give a Get.

Korban Nesan'el (80): The Gemara (28b) explicitly says that one can tell a Shali'ach to appoint someone else to be a Shali'ach to give a Get!

Poskim

Shulchan Aruch (EH 120:4): They scribe may not write and the witnesses may not sign until the husband tells them to. They may not tell others to write and sign. Even if he told Beis Din 'give a Get to my wife', they may not tell a scribe to write and witnesses to sign. Even if he told them to tell a scribe to write and witnesses to sign, the scribe may not write and the witnesses may not sign until they hear from his mouth.

Rema: If he transgressed and divorced via Omer Imru, she is Safek divorced.

Beis Yosef (DH veha'Ro'oh): According to the Ran, R. Yosi is Machshir when the husband himself appointed the scribe and witnesses. If he said Omer Imru and specified the scribe and witnesses, it is Pasul mid'Rabanan lest the Sheluchim deviate. The Ramban holds that both of these are Batel, for they did not hear from the husband's mouth. The Rashba and Rosh agree, and perhaps even the Ran would not be lenient in practice.

Rebuttal (R. Akiva Eiger): The Ran disqualifies Omer Imru mid'Oraisa! He merely explained why R. Yosi allows the husband to appoint Sheluchim in their absence without concern for disaster.