The IRS sends many letters and only a few of them start a clock that cannot be restarted. This article sorts the mail into the categories that matter: notices that are proposals, notices that are demands, and the two notices that carry rights which expire. It explains what a notice of deficiency actually is and why ninety days is the most important number in individual tax practice. It covers the collection notices that open a due process hearing, the collection alternatives that exist and are rarely volunteered, and the relief provisions for people who cannot pay. It follows two fictional taxpayers with the same unpaid balance and very different outcomes. The practical thesis is that almost every catastrophic tax outcome began with an unopened envelope.