Can I ship an item on Friday with overnight shipping?

The Alter Rebbe rules that it is permitted to send mail with a non‑Jew before Shabbos, provided that there is a set price or a commitment to pay (e.g., purchasing a postage stamp or paying for standard postal service). In this manner, the non‑Jew performs the delivery for his own benefit, not on behalf of the Jew.¹

However, this allowance applies only if one does not instruct the non‑Jew to perform the work on Shabbos. Giving such instructions constitutes amira l’nachri, which is prohibited miderabanan, even if the instruction is given before Shabbos.

Furthermore, one may not tell the non‑Jew to ensure that the package arrives by a certain date if it’s unrealistic without traveling on Shabbos. Doing so would, in effect, be directing him to desecrate Shabbos.²

When the non‑Jew could delay the work until after Shabbos, but will perform it on Shabbos, since Sunday is a day off, some poskim are stringent.³ Yet many others are lenient since the gentile’s choice to work on Shabbos is ultimately his own choice. Practically, if he can complete it either before or after Shabbos in a reasonable manner (not by working through the night), there is no need to be stringent.⁴

To place standard mail in a public postal mailbox on Friday before Shabbos—even close to sunset—and the postal worker will transport it on Shabbos is permitted. Since the postal workers operate on their own schedules and the Jew’s involvement ends before Shabbos, there is no issue.

However, even when one has set a price without specifying a delivery time, the non‑Jew may not take the package from the Jew’s property on Shabbos, so that it does not appear as if he was sent on Shabbos (maris ayin). For this reason, one may not leave a package at one’s door for UPS or FedEx to collect it on Shabbos.⁵

Leaving mail in one’s personal mailbox for pickup on Shabbos is likewise an issue of maris ayin (appearance of being sent on Shabbos). Yet others are lenient in cases of need, since it’s known that the mailman is taking his regular route and was not asked to come on Shabbos.

Putting out mail on Shabbos for pickup (whether in one’s own mailbox or in a public box) is certainly forbidden.⁶

See Sources (open PDF)