The quantity of correspondence that is generated by the IRS can be mind boggling.
It is vital to understand each of these notices and act appropriately. The IRS website is a good place to start. There is actually a IRS webpage called Understanding Your IRS Notice or Letter. This page has a list of many of the IRS collection notices.
The IRS notice or letter is more likely than not something that requires immediate attention. There are rights that arise when certain notices/letters come out. For instance when the IRS issues a “Notice of Deficiency” (one type is IRS Letter 3219(SC/CG)) you have 90 days to file a petition in tax court.
If you fail to respond timely you lose rights! Additionally, not attacking the problem at the earliest time period limits possibilities.