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, because the manual answers this itself rather than leaving it to inference. Two sections before the Street Addressing text, the same manual defines what PO Box service looks like in an address:
"Post Office Box, PO Box, or the # symbol when a Post Office street address is used as allowed under 4.5.4, designates this service in an address."
That is the whole answer to the format question, written by the party that assigns the format. The hash version is not a way around PO Box status. It is listed as one of three designators of PO Box service, alongside the words "Post Office Box" and "PO Box." The presentation changed for a human reader. In the system that issued the address, nothing did.
This matters because the parties who screen out boxes are usually not reading your address with their eyes. They run it against address data that carries the classification. A format the classifying authority defines as the same service is not a disguise, and whether a given reviewer treats it as satisfying a physical location requirement is their call, not the Postal Service's. We would not tell you it clears a bank's requirement, because we have no basis to say so.
"Participating locations" turns out to mean something specific
The phrase covers a rule worth knowing, because it decides whether this option is available to you at all. USPS splits PO Box service into two categories, and the split is about competition:
"Competitive PO Box service is available for customers located within the service area of a competitive mailbox service provider. Market-Dominant PO Box service is available to serve customers not served by a nearby competitor."
Street Addressing is not a general feature of PO Boxes. It appears in the manual under the heading "Additional Standards for Competitive PO Box Services," as one of the enhancements available to customers who "may also complete a customer agreement" at those locations.
So the option that makes a PO Box resemble a business address exists where a private mailbox company already operates nearby, and does not exist where none does. It is a competitive response to businesses selling street addresses. There is a practical consequence: because the category is assigned to the location rather than to your account, two Post Offices a few towns apart can differ on this, and the one that says no is not being difficult.
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.
Who the box belongs to is settled by who signs for it
Everything above is about what a form will accept. There is a separate question that surfaces later, usually at an awkward moment: whose box is it? A box rented before the company existed, or rented by one founder while two people were building the thing, has an owner already, and the postal rules are unusually blunt about who that is.
The Domestic Mail Manual settles it in one sentence:
"Box customer applies only to the person who signs the application as an individual or to the organization on whose behalf an individual signs the application."
So the answer was decided at the counter. PS Form 1093, the PO Box application, opens with a required selection between Business/Organization Use and Residential/Personal Use. If you pick the business option, item 2 takes the name of the business or organization and item 3 takes the name of the person applying, with the instruction to "include title if representing a business/organization." Signing as yourself makes you the box customer. Signing on the company's behalf, with the company named and your title on the line, makes the company the box customer and you the person who signed.
Two more items on that form do work people do not expect. Item 9 asks for the names of everyone who will receive mail at the box, "including members of a business." Item 10 asks separately for the people authorized to pick mail up. The manual repeats the requirement for employees and representatives of organizations, and adds an obligation that is easy to miss: "If any information required on PS Form 1093 changes, the box customer must update the application." A box that still lists a departed cofounder as an authorized recipient is not a paperwork detail. It is a current statement to the Postal Service about who may collect your mail.
This is also where two common situations resolve. If someone else has been putting your box number on their own filings, the box record does not make their company a customer of that box, and item 9 is the list that says who was supposed to be receiving mail there. And if you are selling a business whose mail arrives at a box you rented personally, the box does not transfer with the company, because the customer of record is you rather than the entity. Sorting that out is something you do at the counter on a Form 1093. The purchase agreement cannot do it for you.
The transfer rules are narrower than most people assume. Service moves without an extra fee only to a box of the same size and fee group at a different facility of the same Post Office, no more than once in any semiannual payment period, with a completed Form 3575 at the time of transfer and a new application filed at either facility. Moving your company to another city falls outside that rule entirely. It becomes a new application at a new Post Office, at a new fee, with the ownership question asked again from the top.
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. That paperwork is where the trade usually gets expensive: the proof-of-address side of Form 1583 is six checkboxes with no line for a utility bill.
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 do is show you one state's wording in full, because it explains the mechanism that the summaries elsewhere only report as an outcome. Wyoming requires every business entity to continuously maintain in the state:
"A registered office that may be the same as any of its places of business but shall be located at a street address in Wyoming which shall be a physical location where the business entity's registered agent, or a natural person who has an agency relationship with the registered agent, can accept service of process as provided in W.S. 17-28-104 and is physically present at that location"
Only the opening phrase is about formatting. The rest describes a person who is there during business hours and who can be handed a lawsuit. That is why the Street Addressing workaround does not help here, and why it would not help even if the address read perfectly: a box has nobody standing in it. States word this differently and some are less explicit, but once you can see that the test is occupancy, the pattern of what a box can and cannot fill stops looking arbitrary.
Where to look for your own state: 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. For the LLC version of this question specifically, including how the IRS treats a box on Form SS-4 depending on whether it counts you as a U.S. person, we keep a short reference page on whether an LLC can use a PO Box address.
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. The postal standards also treat the two differently once mail starts moving, which we walk through in mail forwarding vs a virtual mailbox. If a box will not clear the field you are filling in, our roundup of the seven biggest providers sorts them by reader type. For the postal rules that keep a PMB address off the PO box category, and the exact way to write one, see Is Your Mailing Address a P.O. Box?.
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. The mechanics of that filing, including where it goes and how long it takes, are in changing your LLC address with the IRS.
The box is in my name but the company uses it. If I sell the business, does the box go with it? Not by itself. The postal manual defines the box customer as the person who signed the application as an individual, or the organization on whose behalf someone signed it. A box you rented personally stays yours even if every piece of mail in it is addressed to the company, so the handover is settled at the Post Office on a Form 1093 rather than by the sale documents. If the company was meant to be the customer, that had to be the selection made on the application at the counter.
Is changing my address with USPS the same as changing it with the IRS? No, and the overlap runs only one way. Telling the IRS does nothing at the Post Office. A postal change can reach the IRS, but only where the records happen to line up: the regulation on a taxpayer's last known address says the IRS updates addresses from the USPS National Change of Address database where the name and old address in its files match the NCOA entry. A business that filed the postal change under a name the IRS carries differently does not match, and the IRS tells taxpayers to notify it directly regardless, noting that not every post office forwards government mail. Form 8822-B is that direct notice, and state filings have their own amendment path on top of it. If the match never happens, the IRS keeps writing to the old address, and you usually learn that from a notice you never received.
