I learned recently that the Mezuzot should be within the first Tefach of the thickness of the doorpost. The Mezuzot that are on both entrances of our building are not within the first Tefach. (This is a jointly owned building.) Do we have to move them to within the first Tefach? They are built into the wall, which makes it a bit more difficult to move, but we could do it if we have to. Does the fist Tefach include the stone of the outside of the building (which is part of the doorpost)? The stone is about 5 centimeters thick. Does the entire Mezuza have to be within the Tefach? How many centimeters is a Tefach?
Though the Mezuzah should be placed in the outer Tefach of the doorway (8-10 cm) the Rama says it does not have to be moved if it was already placed. Rav Ovadia Yosef agrees, but suggests moving it if no hardship will be incurred.