The chametz is in the mail

Hi,

If a Jew sends chametz to another Jew before Pesach, and the package is delayed such that it is in transit during Pesach, neither the sender nor the intended recipient can solve the problem of owning chametz during Pesach by selling it to a non-Jew. This is because neither has access to the package; were the sender to notify the post office that he wanted to rescind the shipment, or were the intended recipient to request that the shipment be re-directed, the post office would not listen.

One who needs to send such a shipment should give it as a full gift to a non-Jew before sending it, and then send it. However, one should not do so when shipping to Israel if it might arrive there during Pesach, since the Jews working in the Israeli mail will be required to accept responsibility for it when it arrives there.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 1:146)

Have a great day,
Mordechai