The Amen for "v'Yatzmach"

Hi,

One who is davening with a Sephardic minyan, so that they include ויצמח פורקניה ויקרב משיחיה, should not respond Amen to those words when he is in pesukei d'zimra. The Rambam did not include an Amen for this line in his edition of kaddish, so it is not considered integral.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:14)

Have a great day,
Mordechai