This article is an excerpt from our Sefer
Intimacy in the spiritual worlds – Sefiros and angels:
Intimacy does not just exist in the physical and spiritual worlds amongst human souls, it also exists amongst the Sefiros. The Sefiros of each world engage in unifications, similar to that of human intercourse and intercourse of souls; they draw down the infinite light of G-d to create souls and angels as a result. More specifically, souls and angels derive from the unity of Ava [i.e. Chochmah with Bina] and Zun [i.e. Zeir Anpin with Malchus]. The Sefiros contain a masculine and feminine aspect which unite and breed the souls of creation. Now, there exists two types of Zivug, one is called Zivug Gufani in which the Yesod unites with the Yesod, and the other being called Zivug Neshikin, which is a unity of Chabad with Chabad. The souls of angels derive from the Zivug Neshikin, which is a Zivug of kissing mouth to mouth, while the souls of the Jewish people derive from the Zivug Gufani. Zivug Gufani is a lot more powerful then Zivug Neshikin, as the Zivug of Neshikin does not carry with it all the aspects and strengths of its parents/Mashpia, while the Zivug Gufani draws down all the powers found in the Parents/Mashpia. Accordingly, Jewish souls carry in them aspects of all the Sefiros and have the ability to reproduce, while the souls of angels are created only from one aspect of the Sefiros and cannot procreate.
Above the world of Atzilus: There is no unification or masculine and feminine aspects above the level of Atzilus. Zivug is only relevant in Atzilus and below, where the Sefiros exist within Keilim.
Angels: In Derech Mitzvosecha, the Tzemach Tzedek writes that angels do not engage in intimacy and cannot procreate. [They do however engage in what is called Zivug Neshikin, which is a unity of Chabad with Chabad.] Elsewhere, however, he writes that in truth there does exist masculine and feminine angels, and that they too engage in intimacy and procreation, although not on the same level as the souls of humans.
 See Tanya Igeres Hakodesh 20; Derech Mitzvosecha Peru Urevu p. 3a-4a; Or Hatorah Bereishis p. 1576
 Derech Mitzvosecha 4a
 Or Hatorah Bereishis p. 220; See Sefer Hama’amarim 5730 p. 229