When you apply for an EIN, the IRS does not ask for one address. It asks for two, on two different lines of the same form, and the two lines follow different rules.
Line 4 is labeled "Mailing address." Line 5 is labeled "Street address." People assume these are the same thing written twice, fill in the same address on both, and move on. Most of the time nothing goes wrong. But the two lines exist because they answer two different questions, and one of them can be a P.O. box while the other cannot.
There is no single statute called "the business mailing address law." This is an administrative concept that shows up on IRS forms, bank paperwork, and state filings, and each of those contexts can ask for something slightly different. The clearest place it is spelled out is the instructions for Form SS-4, the form you file to get an EIN. That is what this page walks through.
What the form actually asks for
Form SS-4 has two address fields near the top.
Line 4a/4b, "Mailing address." The form labels this field "room, apt., suite no. and street, or P.O. box." The words "or P.O. box" are printed on the form itself. A P.O. box is an accepted answer for this line.
Line 5a/5b, "Street address." This field asks for the physical location, and the instructions say directly: "Don't enter a P.O. box number here."
So the form is not asking the same question twice. Line 4 asks where you want IRS mail sent. Line 5 asks where the business is physically located. The IRS uses Line 4 to decide where your EIN confirmation notice, CP575, and later correspondence go. Line 5 is not a mailbox question at all.
If you leave Line 5 blank, most filers repeat the Line 4 address there, which only works if that address is a real street location and not a box. If your only address is a P.O. box, you have to put an actual street address on Line 5, even if it is someone else's office, because the box cannot go there.
This split is not unique to the IRS. Banks, state filing offices, and payment processors each keep some version of the same distinction: an address for mail, and an address for "where are you." They do not all draw the line in the same place, and none of them are bound by what the SS-4 instructions say. But the SS-4 mailing/street split is the most specific, most commonly cited federal reference point for the general idea, which is why it is worth understanding on its own.
🇺🇸 If the IRS counts you as a U.S. person
Nothing about this changes based on your tax residency.
You fill out Line 4 with a mailing address, and a P.O. box, a private mailbox, or a virtual mailbox address all work there. You fill out Line 5 with a real street address, and a box will be rejected regardless of who you are.
If you use your home address as your mailing address, remember that this is a different question from whether that address becomes public through some other filing, such as your state's registered agent record. This page is only about what the IRS accepts on SS-4. It says nothing about what your state publishes.
🌏 If it does not
Nothing about this changes based on where you live, either.
You still fill in Line 4 with a mailing address, and a P.O. box or virtual mailbox address is accepted there in exactly the same way. You still need a real street address for Line 5. Living outside the United States does not add a requirement here and does not remove one. The IRS instructions do not ask where you live, and they do not treat a foreign applicant's SS-4 address lines any differently from a domestic one.
Where your situation is likely to differ from a U.S.-based founder's is upstream of this form: getting a U.S. street address at all to put on Line 5, and getting mail forwarded once it arrives at your Line 4 address. Those are practical problems, not different rules.
What is the same for everyone
| Question | Line 4 (Mailing address) | Line 5 (Street address) |
|---|---|---|
| Can it be a P.O. box? | Yes. The form's own label says "or P.O. box" | No. The instructions say not to enter a box number here |
| What is it for | Where the IRS sends your EIN notice (CP575) and later mail | Where the business is physically located |
| Does citizenship or residency change the rule? | No. The form does not ask, and the rule does not change | No. Same answer for every applicant |
| Can you leave it blank? | No, this line is required | Usually filled in with the street address if Line 4 is a box; cannot itself be a box |
This is the one term in this guide where the answer really is identical no matter which lane you are in. The IRS did not build a residency test into this part of the form. Both lines apply exactly the same way whether the applicant lives in Ohio or Osaka.
Common mistakes
🇺🇸 If the IRS counts you as a U.S. person
- Putting a P.O. box on Line 5 because it was easier than finding a street address. The application can be rejected or corrected back to you, which delays your EIN.
- Assuming Line 4 and Line 5 must match. They often do, but only because the applicant has one address to give. They are legally allowed to be different.
- Never updating Line 4 after moving. The IRS keeps mailing your EIN correspondence to the old address until you file Form 8822-B.
🌏 If it does not
- Assuming a foreign mailing address is not allowed on Line 4. It is allowed; the field does not restrict it to U.S. addresses.
- Using a P.O. box for Line 5 because no other address is available yet, without realizing the application will bounce back for that specific field.
- Treating "I have a mailing address" as the same milestone as "I have a business address a bank will accept." A mailing address that satisfies Line 4 does not automatically satisfy a bank's or a state's separate address requirements.
FAQ
Can my business mailing address be a P.O. box?
Yes, for Line 4 of Form SS-4. The field label itself says "room, apt., suite no. and street, or P.O. box," so a box is an accepted answer for the mailing address line.
Can I use a P.O. box for the street address line instead?
No. The instructions for Line 5 say directly not to enter a P.O. box number there. That line asks for a physical location, not a mailing point.
Is the mailing address rule different for someone who lives outside the United States?
No. Form SS-4 does not ask about residency or citizenship on either address line. A foreign applicant fills in the same two fields, under the same rules, as a U.S.-based applicant.
What does the IRS actually send to my mailing address?
Correspondence tied to your EIN application and account, including the EIN confirmation notice, CP575. If that address changes later, you update it with Form 8822-B rather than waiting for the IRS to notice.
If I only have a P.O. box, what do I put on Line 5?
You need an actual street address for Line 5, since a box is not accepted there. This can be a different address than your P.O. box, such as an office or another physical location connected to the business.
Is there one law that defines "business mailing address"?
No. There is no single statute by that name. The clearest federal reference point is the Line 4/Line 5 split in the Form SS-4 instructions, but banks, states, and other forms can ask for addresses under their own separate rules.
Does my business mailing address show up in public records?
That depends on which filing you are asking about, not on Form SS-4. The EIN application itself is not a public filing. Other documents, such as your state's registered agent record, can make an address public even if it was never entered anywhere on Form SS-4.