You first need to contact the property management company about the water heater and the mail box situation in person as to how the situation will be resolved and follow up with a letter memorializing the conversation, keeping a copy of it for future need and reference.I suggest that given the problems with the water heater a new one is needed to be installed and installed in a prompt manner. As to the mail box situation, that too needs to be resolved in that you need access to your mail.If the property management company fails to respond in a timely and adequate manner to your last contact and request for remedy, you should consult with a landlord tenant attorney about writing a forceful letter to the property management company on your behalf.