The gender of angels-Male versus female:
In Kabala it states that there are angels who come from the level of Za and angels who come from the level of Malchus. Angels who come from Z”a have a masculine aspect, while angels who come from Malchus have a feminine aspect and are called daughters and Nukvin. However, in the Midrash and Poskim it states that there are no female angels and all angels are male. This is learned from the verse “Ir Giborim Ala Chacham” which means that Moshe ascend to the city of angels, and these angels are called Gevarim, thus proving that there are no female angels. Based on this it is ruled in Halacha that women are not to wear white clothing on Yom Kippur to emulate angels, as they cannot be like angels, as angels are only male.
The purpose of the female angels:
Kabala explains that the purpose of the feminine angels who derive from Malchus is to discern the sins committed by people of the world. The Sefirah of Malchus has the function of judging the world, and hence requires information of the acts of the worlds inhabitants. Hashem set up the system in a way that the Sefiros do not automatically know the actions of the creations and need messengers to deliver the information to the Sefiros. This is the function of the female angels; they elevate news regarding the creations to the Sefirah of Malchus. They also carry the blemish caused by sin of the creations into the Sefira of Malchus. On this the verse states “Einei Hashem Mishotetos” in female tense.
 Torah Or Vayeira 15a based on Zohar Mishpatim p. 107
 Yalkut Simoni on Mishlei 21/22 brought in Machatzis Hashekel 610/5
 Admur 610/9; M”A 610/5; Mateh Moshe brought in Machatzis Hashekel ibid
 Mishlei ibid
 Yalkut ibid
 Admur ibid; M“A ibid
 Torah Or Vayeira 15a
 Divrei Hayamim 2 16/9