I just moved into a condo unit in a frum community. (I am a baalat teshuva.) The condo had apparently been abandoned for 7 years prior. There is a very old mezuzah on the wall (not the doorpost) just outside the entryway door of the condo unit. I have no idea if the old mezuzah is kosher, and anyway I have my own mezuzah I want to put on the doorpost itself. Do I need to remove the old mezuzah before install my new one? Anything else I should know about this situation?

Shalom, Thank you for your question. Mazel Tov on your new home. You are correct in thinking that putting up your own Mezzuzah that you know to be kosher is a good idea. Yes, you should remove the old one first – and pass it on to the Rabbi for Geniza (disposal of holy objects). You might want to check with the Rabbi as to the correct placement of the new mezuzah, as it seems strange that the old one was not on the door – perhaps there is some interesting structural building that involves placing the mezuzah not on the doorpost. Or, more likely, the last one was put up incorrectly. In any event a quick video call or visit with a Rabbi will determine the issue. Don’t forget that you need mezzuzot on the other doors of your house also, not just the front door. Many Blessings.