Shulchan Aruch Chapter 247:
The Laws of Sending Out Letters on the Sabbath (6 Paragraphs)
Note:  REMA in brackets [ ]

1.  One is permitted to send a letter through a Gentile and arrange payment even if one forgot to do so until Erev Shabbat (the Eve of Sabbath). This applies only if one does not tell the Gentile "send it out on the Sabbath".  However, if one did not arrange payment or if he is not an established mailman [meaning an individual who is known that that anyone who gives him a letter to be delivered, he delivers] then it is prohibited to send a letter, even on Sunday [1].  If he is an established mailman then it is permitted to send a letter through him on Friday if it is done during the day in order that it would be possible for it to reach the house next to the city wall (before dark).  [There are those who permit even if one did not arrange payment or even if he is not an established mailman as long as one sent him out on Sunday or earlier.  One may rely on them if necessary.]

2.  If one made a deal with the mailman for payment, it is permitted even if he did not specify the amount to be paid.  It has the same law as if one arranged payment since the Gentile's mind is satisfied and he would work on his own accord.  However, sending a postman without any arrangement is prohibited even though the Gentile has in mind that he will get paid.  This is because his mind is not satisfied and will work directly for the Jew's accord. 

3.  Suppose the case where one normally hires the mailman at a daily rate for all of his delivering and returning but does not specify when to go out.  This would be prohibited on Friday, since when the Gentile works on the Sabbath it would appear that the Jew arranged for him to do so. 

4.  If the Gentile delivers to mail for free, then it is permitted to send out mail even on Friday since the Gentile is working on his own accord and would only do the Jew a favor for what he would tip him so it is like one who arranged payment.  [There are those who argue and hold that anytime the Gentile works for free it is prohibited to send him and it is good to be stringent.  However, in a place where the Gentile tells the Jew that he will send it for free but rely on the tip the Jew will fork over, then it is permitted.]

5.  If the Gentile goes on his own accord to another place and the Jew gives him a letter, then it is permitted in all cases.

6.  One who hires a Gentile worker for a year or longer, it is forbidden to send him on Friday to deliver a letter.  [However, if one only hires him to send a letter then there are those who permit it like was explained earlier in Ch. 244.] [2]

[1]  M.B:  If he is not an established mailman, he may not be familiar with the route and be likely to work on the Sabbath.
[2]  The Gentile would not act on his own accord, but will definitely work on the Sabbath to deliver the letter for the Jew.  He will have other work that needs to be done after he sends the letter so he will rush to do it as fast as possible in order that he can do other work for the Jew.  (my interpretation of the Beur Halacha)

Translated by Dr. Jay Dinoviter DO 12/2011
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