Are writings which are forbidden to be read on Shabbos Muktzah?
One is particular about the writing: Any writing which is forbidden for one to read on Shabbos, is [Muktzah Machmas Gufo and is hence] forbidden to be moved if it is of importance in one’s eyes, and he is thus particular against using it as a bottle stopper and the like. [The reason for this is] because it is not fit for any use on Shabbos.
Bills of divorce: Therefore there are opinions which prohibit moving a Kosher bill of divorce [Get”] which one plans to divorce with, as is written in Even Haezer chapter 136 [Halacha 7] look there. However an invalid bill of divorce [“Get”] or a Bill of divorce which was already used to divorce the woman with, is permitted to be moved, as one is no longer particular against using it to stop up a bottle.
One is not particular about the writing: It is permitted to move the letter on Shabbos and it is not forbidden due to Muktzah even if it is not fit on Shabbos for its main benefit, which is to be read, such as when one knows it does not contain matters pertaining to ones bodily [health and security], in which case it is forbidden to even read it in one’s mind. The reason for why it is not Muktzah is because nevertheless it is fit for another benefit, such as to cap a bottle with and matters of the like.
All writings which are forbidden to be read on Shabbos, are considered Muktzah Machmas Issur if they are not of importance for oneself. If however they are of importance, and one would thus refrain from using the paper for purposes which will destroy it in the process, then they are completely Muktzah. [Thus books which are forbidden to be read on Shabbos are Muktzah.]
Letters: Even those letters which are forbidden to be read on Shabbos are not [completely] Muktzah, as it is still fit to be used as a bottle stopper, [rather they are considered MM”I]. Furthermore, even if the letter arrived on Shabbos from out of city limits it is not Muktzah.