May a man send a present to a woman?
A man is to avoid sending gifts to a widow or any single woman. Likewise, some Poskim rule one is to avoid sending gifts to even to a married woman due to Sheilas Shalom. However, when doing so without any intent of affection, such as out of business practice or for a relative, one may be lenient to send gifts to a woman.
 Rama 695:4 regarding Mishloach Manos that men may not send to women as this may lead to sending to a widow [or any single woman-Yifei Levav 5:8] which will cause there to be a question of betrothal. [Rama ibid] The reason this will cause a question of betrothal is because people will think he is sending her the gifts because she is already engaged to him. [M”A 695:15]
 Betzeil Hachochmah 5:51
 The reason: Just as the Sages forbade Sheilas Shalom to a woman [E.H. 21:6] and an Avel [Y.D. 385], so too they forbade sending gifts to an Avel [Rama 696:6] and the same should apply to a woman. [ibid] Vetzaruch Iyun as if so then the Rama should have prohibited sending Mishloach Manos to the opposite gender on Purim due to this reason and not due to a questionable betrothal. See Betzeil Hachochmah for his answer on this subject.
 Betzeil Hachochmah ibid
The reason: As today we are lenient even regarding Sheilas Shalom to a woman, and certainly here regarding a present. [ibid]