I would like to give some people at work mishloach manot. I work at a Jewish company, so we are off on Thursday for Purim. Is it assur to give mishloach manot on Taanit Esther? I know I won’t be yotzei on the mitzvah (I’m giving to more people on Purim Day), but I just wanted to give them something to be nice during Purim time.
Giving mishloach manos is supposed to be done specifically during the daytime of Purim itself. The reason being, is that one of the reasons that we send it, is so that the other person will be able to eat it for the Purim seuda, and if it is sent beforehand it may already be eaten by the time Purim day comes around. However it is not a problem with giving it beforehand, even though your are not fulfilling the mitzvah with this specific mishloach manos, you will fulfill mitzvah with other ones that you will give out on Purim day.
As a side point although you are technically not fulfilling the mitzvah, it is definitely a good thing to do. One of the ideas of mishloach manos is to make other people happy and encouraging friendship. When giving the mishloach manos beforehand you are in a way enhancing the friendship, so even though you cant’ give it on Purim itself it is still a good thing.