LetterAgent
Mail physical letters by just asking your AI assistant.
Yes, you can fax a completed W-9, and plenty of payers still accept one. But a fax is the riskiest common way to move a form carrying your full Social Security number: faxes sit on shared output trays, one wrong digit sends it to a stranger, and nothing encrypts it in transit. Prefer a secure portal; if you must fax, confirm the number by voice first.
This is general information, not tax advice.
| Question | Short answer |
|---|---|
| Is faxing a W-9 allowed? | Yes. The IRS accepts W-9s by any method the payer will take; there is no rule requiring a specific delivery channel. |
| Does the IRS need the original? | No. Payers keep the W-9 on file; they do not send it to the IRS. A faxed or scanned copy is fine as long as it is legible. |
| Does a W-9 expire? | No. It stays valid until your information changes (new name, address, or tax classification), at which point you send an updated one. |
| Biggest risk? | Misdialed numbers. A fax confirmation page only proves a machine answered, not that the right person picked it up. |
Old habits and old software. Many accounting departments built their vendor-onboarding process around fax decades ago, and their checklists still list a fax number as the default. Small businesses without a vendor portal often find fax simpler than setting up secure file sharing for a one-page form. It is not that fax is the best channel; it is that for some offices it is the channel that already works, and nobody has changed it.
There is also a compliance angle worth knowing: payers face backup-withholding penalties if they pay you without a valid taxpayer identification number on file. That pressure makes their AP staff hungry for the form fast, and fax feels fast. Understanding their urgency helps you negotiate a safer channel: offer an encrypted upload link or a password-protected PDF instead, and most will accept.
Three specific dangers, each worth taking seriously.
First, misdials. A fax confirmation page tells you a machine answered at the number you dialed. It does not tell you whose machine. Transpose two digits and your Social Security number, name, address, and signature go to whoever owns the wrong number. Unlike email, there is no recall button and no bounce message.
Second, the output tray problem. Office fax machines print everything that arrives, and the pages sit in the tray until someone collects them. In a busy AP department, your W-9 can wait alongside everyone else's mail, visible to anyone walking past.
Third, no encryption. A fax travels over phone lines or the internet (with internet fax services) as an image, readable at every hop. Email has the same weakness, which is why the safest options are a proper vendor portal with a login, or an encrypted upload the payer hosts themselves.
If the requester will only take a fax, shrink the risk with this checklist:
The payer's own secure vendor portal is the best option: it is encrypted, it is logged, and it puts the file behind a login. Next best is an encrypted file-sharing link you generate yourself (a service that lets you set a password and an expiry on the link), sent separately from the password. A password-protected PDF emailed as an attachment, with the password delivered by phone or text, beats a plain fax too.
What about mailing the W-9? A mailed letter to a US address avoids the misdial risk entirely, and the envelope keeps the form private in transit. It is slower, but for a form you submit once and keep for years, a few days of mail time rarely matters. If you mail it, a letter service can handle the printing and postage from a chat message, with the price quoted up front before anything goes out.
LetterAgent's fax flow works like this: you ask your AI assistant, get a per-fax quote with the page count verified, approve the exact total, pay once through Stripe, and the fax goes out. Only US and Canadian fax numbers are supported, and there are no inbound faxes. One caveat that matters here: fax is currently in testing with activation in progress, so it is described as available in testing and a send cannot be guaranteed today. If your payer needs the W-9 urgently, use one of the safer alternatives above rather than waiting.
Whichever channel you use, the safety rules do not change: confirm the destination, keep the form off shared trays, and keep a dated copy of what you sent.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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