The Ones That Matter Most
CP14: first balance due notice. CP504: warning they may levy. Letter 1058/LT11: final warning before levy with your CDP hearing right (30-day deadline). Notice of Deficiency: 90 days to petition Tax Court or lose the right forever. CP2000: they think you underreported income.
The Rule
Read every IRS notice. Respond by the deadline. Use certified mail. Keep copies. For anything involving significant money or tight deadlines, call a tax professional before responding.
An IRS notice is the opening move in a conversation. How you respond determines whether the conversation ends well or badly.