There are certain circumstances that will allow you to withhold rent in Nevada, typically situations that involve the dwelling being uninhabitable. However, receiving mail may fall into specific categories that would, in the end, give you the right to withhold or at least reduce the amount of rent you are paying until the situation is remedied. Having said this, you do not want to make this your first course of action. Instead, you need to send a certified letter to your landlord asking him to provide you with a key. This will document your issue so that you may provide it to the court should you eventually find yourself in the middle of a lawsuit with your landlord. If your landlord still refuses to provide you a key, I highly recommend retaining an attorney before withholding rent. Once you withhold rent you subject yourself to eviction for breach of your lease. Start with a certified letter and see if that resolves the issue. If you are depending on your disability check in order to help pay rent, then you need to immediately seek the assistance of an attorney before you find yourself in arrears with your rent payments. Best of luck to you.
I am licensed in Nevada. The above information should be construed as legal recommendations only and not legal advice.