Mail letters to the IRS and government agencies
Letters to the IRS, state tax boards, DMVs, and other agencies can be sent as USPS Certified Mail for $12.99 online — the mail class the IRS itself recognizes for timely-filing proof under the "mailbox rule."
Usually the right pick: Certified Mail · $12.99
The IRS runs on postmarks. Under the timely-mailing-as-timely-filing rule (IRC §7502), a document postmarked by the deadline counts as filed on time — and a Certified Mail receipt is the textbook way to prove the postmark date. Responding to a CP2000 notice, filing an amended return cover letter, disputing a penalty: Certified, every time.
The same logic covers most agencies: state tax boards, unemployment offices, the DMV, USCIS correspondence, county recorders. Government mailrooms lose things; your Certified tracking number is what turns "we never got it" into "it was delivered on the 14th at 10:02 am."
Address precision matters more with agencies than anywhere else — the IRS uses different PO boxes by state and by form. Copy the exact address from the notice you received (it is usually printed in the corner), and let the USPS address check confirm it before payment.
One honest caveat: for actual tax returns close to a deadline, weigh e-filing first — it is instant. Physical Certified Mail is for the correspondence e-file cannot carry: notice responses, penalty abatement requests, and anything an agent asked you to mail.
Common questions
Does the IRS accept Certified Mail as proof of filing?
Yes — the Certified Mail postmark date is treated as the filing date under the timely-mailing rule. Keep your receipt with the tracking number; it shows the acceptance date.
Do I need the Return Receipt for the IRS?
Usually the $12.99 Certified option is enough — the postmark proves timeliness. Add the electronic Return Receipt ($14.99) if you also want proof of the delivery date, e.g. for an appeal window.
Which IRS address do I use?
The one printed on the notice you are responding to. IRS addresses vary by state and form type, so always copy from your specific notice rather than a generic list.