If a letter from the IRS just landed in your mailbox, it’s almost always for one of a handful of reasons: you owe a balance, the IRS changed something on your return, third-party income doesn’t match what you reported, the agency needs to verify your identity, your return was picked for review, or the IRS is confirming a change you already asked for. So when people ask why the IRS sends mail, the short answer is that mail is how the agency is legally required to reach you, and the notice number printed on the letter tells you which of those reasons applies to you.
Getting one doesn’t automatically mean trouble. Plenty of IRS letters are routine. But every notice carries a deadline in its text, and those deadlines control your right to dispute a charge or avoid extra penalties, so none of them should sit unopened.
Why the IRS Reaches Out by Mail in the First Place
The IRS makes first contact with taxpayers through the U.S. Postal Service.1Internal Revenue Service. How to Know It’s the IRS Federal law requires written notice before the agency can take certain collection actions, such as placing a lien on your property or levying your bank account. Mail also creates a paper trail that protects you and the IRS if the matter later goes to appeals or court.
That’s why the agency does not initiate contact by email, text message, or social media. If something arrives through those channels claiming to be the IRS, it isn’t.2Internal Revenue Service. Ways to Tell if the IRS Is Reaching Out or if It’s a Scammer
The Reasons Behind an IRS Letter
Nearly all IRS correspondence falls into one of these buckets:
- You have a balance due.
- The IRS made a change to your return.
- Information reported by an employer, bank, or brokerage doesn’t match your return.
- The IRS needs to verify your identity before processing your return or issuing a refund.
- Your return was selected for review or audit.
- The IRS is confirming a change or refund you already requested.
The letter you’re holding will say which. Every IRS notice has an identifier starting with “CP” or “LTR,” usually printed in the upper or lower right corner of the first page. Once you have that number, you know what the letter is asking of you.
The Most Common IRS Notices and What They Mean
CP14: You Owe a Balance
The CP14 is the most common IRS notice. It’s the first letter you get when you owe unpaid taxes, and it states the amount due including penalties and interest. You have 21 days from the notice date to pay before additional interest kicks in.3Taxpayer Advocate Service. Notice CP14 – TAS If the number looks wrong, respond within that window anyway. Silence costs more regardless of whether the original figure was right.
CP2000: Your Income Doesn’t Match Third-Party Records
A CP2000 means the income on your return doesn’t line up with what employers, banks, or other payers reported to the IRS. It is not an audit. It’s a proposed adjustment, and the IRS is asking you to agree, partially agree, or explain. You generally have 30 days to respond, or 60 days if you live outside the United States.4Internal Revenue Service. Topic No. 652, Notice of Underreported Income – CP2000 Common triggers are a forgotten 1099 from freelance work, a brokerage account, or a retirement distribution. If the IRS has it right, you can agree and pay. If a 1099 was issued in error, respond with documentation.
CP21B: The IRS Processed a Change and You Have a Refund Coming
The CP21B is sent after the IRS processes changes you asked for, such as an amended return. If those changes produce a refund, the notice says to expect it within two to three weeks, provided you don’t owe other debts the IRS is required to collect.5Internal Revenue Service. Understanding Your CP21B Notice Check the numbers on the notice against your records before the refund goes out at the wrong amount.
CP504: Notice of Intent to Levy
If earlier balance-due notices go unanswered, the IRS eventually sends a CP504. This is a formal Notice of Intent to Levy, meaning the agency is telling you it plans to seize your wages, bank accounts, or state tax refund to cover what you owe. The CP504 also warns that the IRS may file a federal tax lien, which can damage your credit and interfere with selling property or borrowing.6Internal Revenue Service. Understanding Your CP504 Notice A CP504 is not routine mail. It’s a late-stage letter that shouldn’t be treated like the first one.
Letter 3219: The 90-Day Notice of Deficiency
Letter 3219, the Notice of Deficiency, is one of the most consequential letters the IRS sends. It proposes additional taxes after a correspondence audit and gives you exactly 90 days from the mailing date (150 days if you’re outside the United States) to petition the U.S. Tax Court without paying the tax first.7Taxpayer Advocate Service. Letter 3219, Notice of Deficiency Tax professionals sometimes call it your ticket to Tax Court, because missing the 90-day window means the IRS can assess the tax immediately and your only remaining option is to pay and then sue for a refund.8Legal Information Institute (LII) / Cornell Law School. 90-Day Letter If you get one, treat the deadline as fixed.
CP5071 Series: Identity Verification
CP5071-series notices are sent when the IRS needs to confirm your identity before processing your return. Sometimes the agency suspects someone else filed under your Social Security number; other times it’s a security screen triggered by an unusual filing pattern. The letter tells you to verify online or by phone.9Internal Revenue Service. Understanding Your CP5071 Series Notice Until you verify, your return sits and your refund doesn’t move. If you never filed the return in question, verifying is how you tell the IRS someone may have used your identity.
CP40: Your Account Was Assigned to a Private Collector
The IRS uses private debt collection agencies for certain overdue accounts. Before any collector contacts you, the IRS sends a CP40 telling you your account has been assigned, and the collection agency then sends its own introductory letter. Both letters include a taxpayer authentication number you can use to verify a caller. Legitimate private collectors will never threaten you or demand payment by gift card.10Internal Revenue Service. Private Debt Collection If someone calls claiming to collect for the IRS and you never received a CP40, don’t engage.
What to Do When an IRS Letter Arrives
Open it the day it arrives. Anxiety is why many envelopes sit unopened, and unopened is where small problems turn into large ones. Every notice has a deadline, and most of those deadlines aren’t extended for readers who didn’t read.
Find the notice number in the upper or lower right corner of the first page and look it up on IRS.gov. Then read the whole letter, not just the top. The payment or response deadline, the amount at issue, and your appeal rights are all in the body.
If the notice references changes to your return and the figures look off, request a Record of Account transcript. It shows what you originally filed and any adjustments the IRS made, so you can see where the numbers diverge.11Internal Revenue Service. Transcript Services for Individuals – FAQs Transcripts are available through your IRS online account, by phone at 800-908-9946, or by mailing Form 4506-T.
When you respond, the IRS prefers written replies. Send copies of supporting documents, never originals. Use the return address printed on the notice. Certified mail gives you proof of the send date. Keep copies of the original notice, your response, and anything you enclosed. If the letter lists a direct phone number, that line reaches staff trained on your specific issue and is more useful than the main IRS line.
What Happens If You Ignore the Letter
Ignoring IRS mail makes the problem more expensive and harder to unwind. The failure-to-pay penalty starts at 0.5% of the unpaid tax per month or partial month, up to 25% of the total owed. After a notice of intent to levy, if you still haven’t paid within 10 days, the penalty rate rises to 1% per month.12Internal Revenue Service. Failure to Pay Penalty Interest also runs on the unpaid balance (currently 7% annually for individuals, adjusted quarterly) and compounds daily.13Internal Revenue Service. Quarterly Interest Rates
Beyond the money, ignoring notices lets the IRS use its enforcement tools. After the CP504, the agency can seize wages, bank accounts, Social Security benefits, and other property.6Internal Revenue Service. Understanding Your CP504 Notice Ignore a Letter 3219 and you lose your right to challenge the proposed tax in Tax Court without first paying it in full.8Legal Information Institute (LII) / Cornell Law School. 90-Day Letter
One limit works in your favor: the IRS generally has three years from the date you filed to assess additional tax. Exceptions apply for fraud, failing to file, and substantially understating income, but for most taxpayers, a notice arriving four or five years after filing likely falls outside that window and may be worth disputing on statute-of-limitations grounds.14Office of the Law Revision Counsel. 26 U.S. Code 6501 – Limitations on Assessment and Collection
How to Tell the Letter Is Really From the IRS
Legitimate IRS mail arrives through the postal service, on official letterhead, with a specific notice or letter number. If you’re unsure, log into your IRS online account at IRS.gov. The Notices and Letters section shows digital copies of most notices sent to you, with the CP number and subject line.15Internal Revenue Service. Online Account for Individuals – Frequently Asked Questions Not every notice shows up there, so keep checking physical mail too, but a suspicious letter that doesn’t appear in your account is a strong signal it may be fake.
A few scam patterns to watch for:
- Demands for immediate payment by gift card, wire transfer, or cryptocurrency. The IRS never accepts these.
- Threats of immediate arrest or pre-recorded voicemails warning of a warrant.
- Unsolicited calls demanding payment. IRS agents may call about a scheduled appointment or an ongoing audit, but only after you’ve received written notice first.
If the letter checks out and you owe more than you can pay right now, the IRS offers short-term extensions and installment agreements you can apply for online, and lower-income taxpayers may qualify for free representation through a Low Income Taxpayer Clinic listed in IRS Publication 4134.16Internal Revenue Service. Payment Plans; Installment Agreements17Taxpayer Advocate Service. Low Income Taxpayer Clinics (LITC) The point of the letter is to give you options while a deadline is still open. Use the time it gives you.