633. Giving Work to a Non-Jew Before Shabbos
Shabbos 6:19
A Jew may not give utensils to a non-Jewish artisan to craft on Friday, even if the craftsman has a set price for the job, unless there is time to pick the articles up before Shabbos. Similarly, a Jew may not sell, lend, pawn, or make a gift of his property to a non-Jew unless the non-Jew can remove the item from the Jew's house before Shabbos. This is because as long as the non-Jew is in the Jew's house, no one knows when the Jew gave him the object. Therefore, if the non-Jew were to leave with the item on Shabbos, it would appear that the thing was being lent, pawned, handed over to be worked on, or sold on Shabbos.
Shabbos 6:20
Let’s say that a Jew gave a non-Jew a letter to deliver to another city. If there’s a set fee for this service, it is permitted even if the Jew gave him the letter on Friday afternoon, as long as the non-Jew leaves the Jew's house before Shabbos begins. If a fee was not set but there is a designated person in the city who collects letters and delivers them to other cities through his agents, then it is permitted to give the letter to a non-Jew as long as there is enough time for it to reach a house opposite the city wall before Shabbos begins, which is the farthest away that the home of the non-Jew who handles the mail delivery might be. If there is no designated mail official and the non-Jew to whom the Jew gives the letter is the one who will deliver it to the other city, then it is always prohibited to send a letter without fixing the price in advance.