The IRS sends mail because federal law requires it to notify you in writing before changing your account, requesting information, or taking collection action, and because a mailed notice creates the paper record both sides need if the matter is ever disputed. A letter in your mailbox does not automatically mean trouble. It may confirm a change you asked for, flag a small balance, ask you to verify your identity, or propose an adjustment the agency wants you to agree with or explain. The notice number printed on the first page tells you which of those it is.
Why the Agency Uses Postal Mail at All
The IRS makes first contact with taxpayers through the U.S. Postal Service.1Internal Revenue Service. How to Know It’s the IRS It does not open a case by email, text, or social media. The reason is partly legal: before the IRS can place a lien on your property or levy a bank account, it has to give you written notice and a chance to respond. The reason is also practical. A dated letter sent to your address of record gives you a clear deadline, gives the agency proof of delivery, and gives any later appeals officer or judge something concrete to look at.
That means every piece of IRS mail is doing one of a small number of jobs. It is telling you about a balance, telling you about a change to your return, asking for missing information, telling you a return was selected for review, or confirming something you already requested. Once you know which job the letter is doing, the rest of it reads much more easily.
The Reasons Behind the Most Common Letters
You Owe a Balance
The most common IRS notice is the CP14, and its job is to tell you the agency’s records show unpaid tax. It states the amount, including penalties and interest, and gives you 21 days from the notice date to pay before more interest accrues.2Taxpayer Advocate Service. Notice CP14 – TAS If you think the figure is wrong, you still need to respond inside that window; silence does not pause the clock.
If earlier balance notices go unanswered, the mail escalates. A CP504 is a formal Notice of Intent to Levy, warning that the IRS plans to seize wages, bank funds, or a state tax refund to cover the debt, and that a federal tax lien may be filed against your property.3Internal Revenue Service. Understanding Your CP504 Notice A CP504 is not routine mail. It means earlier letters did not get a response.
Your Reported Income Doesn’t Match Third-Party Records
A CP2000 arrives when the income on your return does not line up with what employers, banks, brokerages, or other payers reported to the IRS under your Social Security number. It is not an audit. It is a proposed adjustment, and you have 30 days to agree, partly agree, or explain the gap (60 days if you live outside the United States).4Internal Revenue Service. Topic No. 652, Notice of Underreported Income – CP2000 Common causes are a forgotten 1099 from freelance work, a brokerage statement, or a retirement distribution. If the third-party form was wrong, you respond with documents showing why.
The IRS Changed Something on Your Return
A CP21B goes out after the IRS processes changes you asked for, such as an amended return. If the changes produce a refund, the notice tells you to expect it in two to three weeks, assuming no other federal debt is offsetting it.5Internal Revenue Service. Understanding Your CP21B Notice Compare the numbers on the notice against your own records before the refund posts, in case the adjustment was applied differently than you expected.
The IRS Needs to Confirm You’re You
CP5071-series letters are identity verification requests. Sometimes the agency suspects someone else used your Social Security number to file; sometimes a security filter flagged something unusual about the return. Until you verify, through the online tool or by phone as the letter directs, your return will not finish processing and any refund is held.6Internal Revenue Service. Understanding Your CP5071 Series Notice If you did not file the return at all, completing the verification is how you tell the IRS that.
An Audit Produced a Proposed Deficiency
Letter 3219, the Notice of Deficiency, is the most consequential piece of IRS mail most people will ever receive. It proposes additional tax after a correspondence audit, and it gives you exactly 90 days from the mailing date (150 days if you are outside the United States) to petition the U.S. Tax Court to challenge the amount without paying it first.7Taxpayer Advocate Service. Letter 3219, Notice of Deficiency Practitioners call it the ticket to Tax Court for a reason: miss the 90 days and the IRS can assess the tax, after which your only route to contest it is to pay in full and sue for a refund.8Legal Information Institute (LII) / Cornell Law School. 90-Day Letter The deadline on this letter is not negotiable.
A Private Collector Has Been Assigned
The IRS uses private debt collection agencies for certain long-overdue accounts. Before any private collector calls, the IRS mails a CP40 notice telling you the account has been assigned, and the collection agency sends its own introductory letter. Both include a taxpayer authentication number for verifying who you are speaking with.9Internal Revenue Service. Private Debt Collection If no CP40 ever arrived in your mail, no legitimate private IRS collector should be calling you.
What to Do First When a Letter Arrives
Open it the day it arrives. Letters sitting unopened on a counter are how small problems become expensive ones, because almost every notice contains a deadline and most of those deadlines are not extended for taxpayers who did not read the mail in time.
Find the notice number. It is printed in the upper or lower right corner of the first page, and it tells you exactly which of the categories above you are dealing with. Read the entire letter, not just the opening paragraph. The amount in question, the response or payment deadline, and your rights to appeal or petition are all stated in the body of the notice.
If the figures do not match what you remember filing, request a Record of Account transcript. It shows both your original return and any adjustments the IRS made, so you can see where the two diverge.10Internal Revenue Service. Transcript Services for Individuals – FAQs You can pull transcripts through your IRS online account, by phone at 800-908-9946, or by mailing Form 4506-T.
When you respond, write back using the return address on the notice. Include copies of your supporting documents, never originals. Keep a copy of everything you send, and if you mail your response, certified mail gives you proof of the date it went out. The phone number on the notice connects to staff trained on your specific issue; it is more useful than the general IRS line.
Verifying the Letter in Your Online Account
If you want to confirm a letter is genuinely from the IRS, log into your account at IRS.gov. The Notices and Letters section shows digital copies of most of what the agency has sent you, including the CP number and subject.11Internal Revenue Service. Online Account for Individuals – Frequently Asked Questions Not every notice appears there, so a letter missing from the account is not automatic proof of a scam, but a suspicious letter that also fails to show up online is a strong warning sign.
How to Tell IRS Mail From a Scam
Legitimate IRS correspondence arrives on official letterhead through the postal service and carries a specific notice or letter number. The IRS does not open contact by email, text message, or social media asking for personal or financial information.12Internal Revenue Service. Ways to Tell if the IRS Is Reaching Out or if It’s a Scammer An email or text claiming to be the IRS and asking you to click a link, verify your identity, or claim a credit is a scam.
A few patterns reliably mark a message as fake:
- Demands for payment by gift card, wire transfer, or cryptocurrency. The IRS does not accept any of these.
- Threats of immediate arrest or a warrant if you do not call back. The IRS does not leave voicemails like that.
- Unsolicited phone calls demanding payment from someone who never received a written notice first.
If you are ever unsure whether a letter is real, the two best checks are to look it up by notice number on IRS.gov and to see whether it appears in your online account. Both are free, and both take minutes.
One last point worth keeping in mind. The IRS generally has three years from the date you filed a return to assess additional tax, with exceptions for fraud, failure to file, or substantially understated income.13Office of the Law Revision Counsel. 26 U.S. Code 6501 – Limitations on Assessment and Collection A notice arriving four or five years after the return it refers to may fall outside that window, which can itself be grounds to dispute what the letter asks for.