http://revach.net/article.php?id=2012

Section: Halacha   Category: Tshuvos
Rav Shlomo Zalman Auerbach: Can You Give A Check For Matanos L'Evyonim?
The Mitzva of Matanos L'Evyonim is mainly meant to make sure that the poor people have enough to eat for Purim Seudah.  Considering this can you give a check for Matanos L'Evyonim?  Rav Shlomo Zalman Auerbach in Halichos Shlomo (2:19:23) says you can be yotzei with a check even if the bank is closed that day.  Moreover he says you can even give a post dated check.  The reason is that people use checks as cash to pay the grocery and other bills so the check itself is useable and considered money for this purpose.

If a poor person owes you money, says Rav Shlomo Zalman, by simply being mochel him you are not yotzei Matanos L'Evyonim.  You must give him money.

Disclaimer: We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. Please also understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.