Giving a gift involves a transfer of ownership and is thus similar to a transaction. Accordingly, it is generally forbidden to give gifts on Shabbos. On Yom Tov, however, it is permitted to send many types of items as gifts. The reason is that since the sender derives pleasure from sending a gift, he is deemed to be fulfilling the mitzvah of rejoicing on Yom Tov! The only restriction on sending a gift on Yom Tov is that when an unfinished product is sent as a gift, it must be possible for the recipient to prepare it for use on Yom Tov. For example, one may send a cut of raw meat as a gift, since the recipient is able to cook it on Yom Tov. This is permitted even if the sender knows that the receiver will not use the meat on Yom Tov. However, it is forbidden to give a child a toy that needs to be assembled (assuming the assembly would violate a melacha), since the toy cannot be made for use on Yom Tov.
A finished product may be sent as a gift even if its use is precluded on Yom Tov. For example, it is permitted to send Tefillin as a gift, even though they are not worn on Yom Tov. In all the above cases it is permitted to carry the item through a public domain. Its delivery is considered a Yom Tov need, even though the item will not actually be used on Yom Tov, since by delivering it the sender fulfills the mitzvah of rejoicing on Yom Tov. [Note: The following elucidation is offered by the Artscroll Schottenstein Talmud - Beitzah 15a2 in footnote #13: The reason that it is permitted to send tefillin, despite the fact that they have no Yom Tov use, is because the mere sending and receiving of gifts make a person joyful and are thus considered a Yom Tov need. Presumably, only ready-to-use gifts – i.e. finished products, such as Tefillin - cause the degree of joy that elevates sending and receiving to the level of a Yom Tov need.]
This lesson is Hashem’s gift to me and you!