Sending regards to a woman:[1]

A man may not ask a woman at all as to her wellbeing.[2] This applies even if one does so indirectly, through a messenger. It is forbidden to send greetings even through the woman’s husband.[3] [Thus, a man may not ask someone to send his regards to that person’s wife or any woman, or have him ask her on his behalf as to how she is doing. However, it is permitted to do so out of common courtesy that does not contain affection, such as if she was sick he may ask the husband to ask her how she is doing.[4] The above law applies equally to a woman sending regards to a man.[5]]

Inquiring as to the well-being of a woman:

It is permitted to ask a husband as to the wellbeing of his wife.^[6] One may thus ask him “How is your wife doing?”[7] Furthermore, some Poskim^[8] rule it is permitted to ask any man as to the wellbeing of any woman, even if it is not his wife. Other Poskim^[9] however rule it is forbidden to ask other men as to the wellbeing of a woman, and doing so is only permitted to the husband of the woman.[10] [It is permitted to do so however out of courtesy, such as to inquire regarding one who is sick and the like, or in order to prevent animosity or bad feeling.[11] The above law applies equally to a woman sending regards to a man.[12]]

Writing a letter:

When writing a letter to a man, it is permitted to include in the heading of the letter also his wife, and to ask as to his wellbeing and the wellbeing of his wife. It is however forbidden to conclude the letter with asking the man to send regards to his wife.[13] If however she was not feeling well, it is permitted to conclude the letter with an inquiry of her wellbeing [even though the husband will ask his wife that so and so asked how you are feeling[14]].[15] It is however customary not to address the wife by her first name in the letter.[16]

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[1] Michaber E.H. 21/6; Shmuel Kiddushin 70b

[2] The reason: As this can lead to them being acquainted with each other which can lead towards an affectionate relationship. [Rashi ibid; Chelkas Mechokek 21/7; Aruch Hashulchan 21/8] Alternatively, the reason is because the voice of a woman is considered an Erva. [Kiddushin 70a and Brachos 24a, brought in Ezer Mikodesh 21/6 and Aruch Hashulchan 21/8] Now, although in general we rule that the voice of a woman is not an Erva unless she is singing [Admur 75/6 in understanding of Rama 75/3; M”A 75/6 in name of Lechem Chamudos Brachos 3/117; Beis Shmuel 21/4; Michaber 75/3 “Kol Zemer”; Rashba, brought in Beis Shmuel ibid; Yireim 392; Rabbeinu Yona Brachos 25b] nevertheless, her voice that comes as a response to a greeting is considered an Erva. [Rashba, brought in Beis Shmuel ibid; Elya Raba 75/5; P”M 75 A”A 6; Kaf Hachaim 75/22]

[3] The reason: As sending regards creates affection between the two. [Taz 21/1 “It appears to me this is because it shows affection when sending regards”; See Chelkas Mechokek 21/7]

[4] See Taz 21/1 and Beis Shmuel 21/13 that it is permitted in a time of need to ask of her wellbeing, such as if she is ill and one desires to know how she is doing; So rules regarding Sheilas Shalom, and the same would apply regarding sending regards: Ritva Kiddushin ibid, brought in Pischeiy Teshuvah 21/3; Aruch Hashulchan 21/8 in name of Ritva; Pnei Yehoshua on Kiddushin ibid; Maharam Shick E.H. 53 that the world is accustomed like Shmuel [ruled in Rama 21/5]  that whatever one does Lesheim Shamayim is permitted; Taharas Yisrael 21/6-16; Minchas Yitzchak 8/126

[5] Betzeil Hachochmah 5/49

[6] Michaber E.H. 21/6; Baba Metzia 87a

The proof: This can be learned from the fact that the angels asked Avraham Avinu as to the wellbeing of his wife. [Beis Shmuel 21/13]

[7] Chelkas Mechokek 21/7 “Mah Shalom Hagiveret”

[8] Bach 21, brought in Beis Shmuel ibid and Chelkas Mechokeik 21/7; Shaiy Lemorah in defense of Bach that the Gemara never intended to forbid asking others, and simply stated that it is not Derech Eretz to ask others who are not her husband, although there is no prohibition involved.

[9] Beis Shmuel 21/13; Chelkas Mechokeik 21/7; Based on Baba Metzia ibid that states “A husband is different”

[10] The reason: As the man may tell the woman that this man inquired about her and this can create affection between the two. [See Chelkas Mechokek 21/7]

[11] So rules regarding Sheilas Shalom, and the same would apply regarding ending regards: Ritva Kiddushin ibid, brought in Pischeiy Teshuvah 21/3; Aruch Hashulchan 21/8 in name of Ritva; Pnei Yehoshua on Kiddushin ibid; Maharam Shick E.H. 53 that the world is accustomed like Shmuel [ruled in Rama 21/5]  that whatever one does Lesheim Shamayim is permitted; Taharas Yisrael 21/6-16; Minchas Yitzchak 8/126

[12] Betzeil Hachochmah 5/49

[13] Bach 21, brought in Beis Shmuel 21/13 and Chelkas Mechokeik 21/7

[14] Pashut, as otherwise there is no novelty in the Taz’s ruling

[15] Taz 21/1, brought in Beis Shmuel ibid

[16] Rashal, brought in Taz ibid