One must send mishlo’aĥ manot and give matanot la-evyonim on Purim day, as it says, “To observe them as days of feasting and joy, and as an occasion for sending gifts to one another and presents to the poor” (Esther 9:22). If one gives these gifts on the night of Purim, he does not fulfill his obligation.
If one cannot find poor people to receive matanot la-evyonim on Purim, he should set aside his gifts and save them until he finds poor people. Thus, he fulfills the mitzva by the very act of setting the gifts aside. Similarly, a gabbai tzedaka who does not manage, on Purim, to distribute all the funds he collected should distribute them to the poor after Purim (sa 694:4).
However, the mitzva of mishlo’aĥ manot applies only on the day of Purim itself, as that is when there is a mitzva to increase love and happiness between friends. Therefore, if one is alone on Purim and has no one to receive his mishlo’aĥ manot, he cannot compensate for the mitzva after Purim. But now that we have telephones and internet, one may call a friend or write an e-mail and ask him to send mishlo’aĥ manot on his behalf on Purim, thus fulfilling one’s obligation.
One who is concerned that he will not find poor people on Purim may give money to the gabbai tzedaka before Purim, but the giver must stipulate that he maintains ownership over the money until Purim. Then, the gabbai acts as his shali’aĥ and gives the money to two poor people on Purim day on his behalf. Similarly, one who will be alone on Purim may prepare mishlo’aĥ manot in advance, leave them with a friend, and appoint him as his shali’aĥ to give them to another friend on Purim, on his behalf.
. ma 694:1 quotes Ha-ma’or as saying that one must not give matanot la-evyonim before Purim, lest the recipients consume them before the holiday. This implies that if the poor people eat the food purchased with such gifts on Purim, the giver discharges his obligation. Pri Megadim ad loc. comes to the same conclusion. However, Maĥatzit Ha-shekel seems to maintain that one must give the gifts specifically on the day of Purim, and bhl 694:1 cites this opinion. Furthermore, there is uncertainty about what the law is in a case in which one sends mishlo’aĥ manot before Purim but they reach the recipient on Purim: Yad Aharon states that one fulfills one’s obligation in such a case, but Torah Lishma §188 maintains that one does not fulfill one’s obligation, because one must increase love on the day of Purim specifically. ahs 695:16 rules according to the latter opinion with regard to both mishlo’aĥ manot and matanot la-evyonim. There is further uncertainty in a case where one gives the gifts before Purim, telling the recipient that they are merely a deposit until the day of Purim. Mahari Algazi maintains that such a person fulfills his obligation, whereas Devar Eliyahu §69 maintains that he does not fulfill his obligation, because both types of gifts must be given on the day of Purim. If, however, one sends these items via a shali’aĥ on Purim, he discharges his obligations according to all opinions.