Question: Based on what was published yesterday in the “Halacha Yomit” that the Mezuzah should not be placed lower than the top third of the doorpost, I just realized that in my house, the Mezuzah was placed lower than the top third so that the children would be able to kiss it. What should I do?
Answer: Indeed, the Mezuzah must be affixed at the beginning of the top third of the doorpost. We must nevertheless point out that if it was affixed any higher than this point, one fulfills one’s obligation as long as there is still a little more than eight centimeters (approximately 3.1 inches) between the Mezuzah and the top of the doorpost. One who acts stringently and affixes the Mezuzah precisely at the beginning of the top third of the doorpost is especially praiseworthy. (Halichot Olam, Volume 8, page 253)
Regarding the above question, if one has affixed the Mezuzah lower than the top third of the doorpost, such as one who has affixed the Mezuzah to the mid-point of the doorpost so that the children are able to kiss the Mezuzah, and now realizes that this custom is mistaken, one must certainly remove the Mezuzah and reaffix it in the correct place which is at the beginning of the top third of the doorpost.
Maran Rabbeinu Ovadia Yosef zt”l writes that since according to Maran Ha’Shulchan Aruch one who affixes the Mezuzah anywhere lower than the top third of the doorpost has not fulfilled one’s obligation, one who has mistakenly done so and now removes the Mezuzah to affix it to precisely the top third of the doorpost must recite the blessing of “Asher Kideshanu Be’Mitzvotav Ve’Tzivanu Likbo’a Mezuzah” since until now, the Mezuzah was affixed in a halachically invalid manner (ibid. page 257).
Similarly, if one mistakenly affixes the Mezuzah to the left doorpost when entering the house, just the opposite of the well-known Halacha that the Mezuzah must be affixed to the right doorpost when entering the house, and now realizes one’s error, one must remove the Mezuzah and reaffix it on the correct side while reciting the blessing before doing so since the Mezuzah was affixed in a halachically invalid manner until this point.
Summary: If one mistakenly affixed the Mezuzah lower than the top third of the doorpost or if one affixed the Mezuzah to the left doorpost as opposed to the right, one must remove the Mezuzah and reaffix it in the correct place while reciting the blessing of “Asher Kideshanu Be’Mitzvotav Ve’Tzivanu Likbo’a Mezuzah” before doing so.