The question gets asked as if there were one answer. There isn't. A PO box is fine in some places, quietly fatal in others, and the boundary does not run between institutions. It runs between fields on the same page.
The clearest illustration is a form most founders fill out in their first week.
The IRS puts both answers on one form
Form SS-4 is how you get an EIN. It asks for an address twice.
Lines 4a and 4b are the mailing address. A PO box is acceptable there, which is why so many people conclude that the IRS is relaxed about this.
Lines 5a and 5b are the street address, and the instructions are blunt about what goes there. You provide the physical address only if it differs from the mailing address, and the instruction says: "Don't enter a P.O. box number here."
One form. Two address lines. Opposite answers. If you have ever wondered why one accountant tells you a PO box is fine and another says it will cause problems, this is usually why. They are talking about different lines.
The lesson generalizes. Before asking whether a PO box works, ask what the field is for. A field that exists to route mail will take a box. A field that exists to locate you will not.
Banks are the strict end, and it was decided on purpose
The Customer Identification Program rule tells a bank what it must collect before opening an account. For a business, the address it wants is a principal place of business, a local office, or another physical location.
A PO box is none of those. That is where the exclusion comes from, and it is worth knowing how settled it is: when the rule was being written, a trade association representing credit card banks argued that customers "may have a legitimate reason for handling correspondence through post office boxes and should not have to provide a physical address." The agencies declined. The single accommodation they wrote in covers people who have no physical address at all, such as service members, who may give an Army Post Office or Fleet Post Office box number instead.
So the banking answer is not a policy any individual bank invented, and arguing with a branch manager will not move it. We went through what banks must collect, and where the discretion actually sits, in our piece on opening an account without a physical address.
The part almost nobody knows: USPS will let a PO box look like a street address
Here is where the topic gets genuinely confusing rather than just misunderstood.
USPS offers an option called Street Addressing. At participating locations a box holder can complete a customer agreement and then use the Post Office's own street address as their mailing address, with the box number written after a hash. The manual gives the format directly:
John Smith 123 Main Street #4567 Any Town, NY 10001
That address will pass a form that rejects the words "PO Box." It also lets you receive packages from private carriers at the Post Office, which a plain box cannot do.
Read what changed and what did not. The presentation changed. The underlying thing is still a Post Office box, and the building at 123 Main Street is a Post Office rather than a place where your company does anything. Whether a given reviewer treats that as satisfying a physical location requirement is their call, not the Postal Service's, and we would not tell you it clears a bank's requirement because we have no basis to say so.
If your reason for wanting a PO box was privacy rather than mail volume, this option solves the cosmetic half of the problem and leaves the substantive half exactly where it was.
What a mail center address is, in postal terms
The alternative most founders end up at is a commercial mail receiving agency. The postal manual defines it plainly: a CMRA is a business that, in whole or in part, accepts delivery of US Mail on behalf of another person or entity as a business service. Office business centers fall under the same definition for postal purposes.
The practical difference from a PO box is that the address is a real commercial building with a unit number, and mail is accepted there by a business rather than held in a rented slot at a Post Office. That is why this category clears the federal physical location requirement where a box does not. It comes with its own paperwork, including Form 1583 for you and Form 1583-A for the operator, which is the trade you are making.
This is the category our mailbox falls into, and we would rather you understand the distinction than take our word for the outcome.
State filings deserve their own check
Formation documents ask for addresses too, and the requirements are set state by state rather than federally. Some states are explicit about needing a street address for a registered office or agent, others are not, and a few draw the line differently for the registered agent than for the business itself.
We are not going to tell you what all fifty do, because that claim would be wrong somewhere. What we can tell you is where to look: the filing instructions for your state of formation, on the line for the registered agent specifically, since that is the line most likely to reject a box. If you are weighing whether to use an agent's address more broadly, that is its own decision with consequences past the filing.
A short way to decide
Look at what the field is asking for rather than what it is called. A field that exists to route mail takes a box. A field that exists to locate the business generally does not, and that includes physical location, principal place of business, and registered office lines.
If a form gives you both lines, fill in both honestly. Putting the same address on the mailing line and the street address line is what creates the mismatch that gets flagged later.
And if you already filed something with a PO box in a physical address field, fix it at the source rather than waiting for the denial. The IRS has Form 8822-B for a change of business address, and state filings have their own amendment path. Correcting a filing is routine. Explaining an inconsistency after an application has stalled is not.
FAQ
Can I use a PO box as my business address? For mail, yes. For fields that ask for a physical location, generally no. The IRS demonstrates both answers on Form SS-4, which takes a box on the mailing address lines and instructs you not to enter one on the street address lines.
Will USPS Street Addressing let me use a PO box as a street address? It lets you write it in street format with a hash and the box number, and it lets you take carrier deliveries at the Post Office. It does not turn the box into a place where your business operates, and each reviewer decides for itself what that format satisfies.
Why do banks refuse PO boxes when the IRS does not? Because they are collecting different things. The IRS wants somewhere to send mail and, separately, where you physically are. The bank rule asks for a physical location as part of identifying the customer, and the request to let post office boxes count was raised while that rule was being written and not adopted.
Is a virtual mailbox address the same as a PO box? No. A commercial mail receiving agency address is a street address at a commercial building with a unit number, and the postal manual defines the category separately from box service. That difference is exactly why it clears requirements a box fails.
I already used a PO box on my EIN application. What now? If it went on the mailing address lines, that is what those lines are for. If it went on the street address lines, file Form 8822-B to report the change rather than leaving the record inconsistent.
