This Halacha is an excerpt from our Sefer
Greeting a friend:
It is forbidden to greet a friend on Tisha B’av. Thus, one may not greet a friend with Shalom Aleichem [or good morning]. If one’s friend will be offended if he is not greeted, then one is to explain to him the concept of this prohibition.
Responding to a greeting: If one is greeted by another person using the above terms, he should answer the person in a mournful tone.
What is defined as a greeting?
Some Poskim rule that only statements which include the word Shalom are defined as a greeting, and hence greetings such as good morning and the like are permitted. Other Poskim rule that any greeting is defined as a greeting even if it does not include the word Shalom. Practically, one is not to recite any greeting even if it does not contain the word Shalom. This prohibition includes the following phrases:
May one wish a friend Mazal Tov?
May one shake hands with a friend?
One may do so in the process of wishing Mazal Tov to a friend. [However, it is forbidden to do so as a greeting.]
May one say good night?
Yes. However, some avoid doing so.
May one say a Mi Shebeirach for a Yoledes/woman who is after birth?
The Mi Shebeirach is to be said by Mincha, and not by Shacharis.
 Michaber 554:20
 M”B 554:41
 M”B 554:42
 Michaber ibid
 Leket Yosher 110; See Beir Heiytiv 385:2 and Gilyon Maharsha [regarding after Shloshim], that good morning is not considered Sheilas Shalom, as can be learned from Admur 89:3 and Beis Yosef in name of Riy; Likewise, the Darkei Moshe 89 states that it is only considered Shalom if one mentions Hashem’s name; See Beir Moshe 4:100
 Elya Raba 554:20; P”M 554 A”A 21; Shaareiy Teshuvah 554:16; Maharam Shick 370; M”B 554:41; Kaf Hachaim 554:90
 Gesher Hachaim 21:7-5; p. 225; Betzeil Hachochmah 5:75; Nitei Gavriel 107:2; See Pnei Baruch 15 footnote 27
 Ritva Moed Katan 27b; Pnei Baruch 16 footnote 27; Nitei Gavriel 89:7
 Ritva Moed Katan 27b
 Salmas Chaim 422
 Lehoros Nasan 2:37; Az Nidbaru 13:6; Piskeiy Teshuvos 554:19
 Poskim ibid
 Leket Yosher brought in Nitei Gavriel p. 436; However see Nitei Gavriel 56:3 that plainly writes it may not be said.
 The Leket Yosher ibid writes that although it may be said and is not included in “Sheiolas Shalom” nevertheless the Terumos Hadeshen did not do so. See also Nitei Gavriel 56:3 who plainly writes it may not be said.
 Drashos Maharil Tisha Beav; Kaf Hachaim 559:40; Piskeiy Teshuvos 559:6