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A vendor onboarding letter is your first formal mail to a new supplier: welcome them, state your payment terms, name your key contacts, and list what you need before ordering. Keep it to one page and lead with the practical stuff. And don't request banking details in it: account numbers belong in a secure channel, not a paper letter.
| Section | What to write |
|---|---|
| Welcome + introduction | Your company name, what you do, and why you chose them. Two sentences: this isn't a brochure. |
| Payment terms | State the terms up front (Net 30, 2/10 Net 30, etc.), your payment method of choice (check, ACH, wire), and your payment run schedule: e.g. "we pay vendor invoices every other Friday." This single detail prevents more confusion than anything else in vendor relationships. |
| Key contacts | Named people with roles: who approves POs, who handles AP questions, who to call about shipping problems. Include direct phone numbers and emails, not a generic info@ address. |
| What you need from them | The checklist: completed W-9 (US vendors) or tax forms, their payment terms and accepted methods, their primary contact for orders, and their return/shipping policy. |
| How ordering works | Where to send POs (email address or mailing address), the PO format you require, and who to contact about order status. |
Paper mail passes through a lot of hands: your printer, the postal system, their mailroom, possibly a scanning vendor. Banking details on paper become banking details in half a dozen places you can't control, and business payment fraud overwhelmingly starts with intercepted account information, not with bad websites. Here's the safe pattern: use the letter to say that you need their direct-deposit information, then give them a secure channel to provide it: a phone call to your AP contact, or a secure vendor portal. The letter announces the need; the channel collects the details.
Also watch for the reverse scam: if a "vendor" writes to you asking you to change where you send payments, verify it by phone at a number you already have on file: not at a number printed in the letter. Payment-redirection fraud works exactly this way.
Email works for the routine version. Mail earns its place when the vendor relationship is significant: a large contract, an exclusive supplier, or a vendor whose own paperwork is paper-based. A mailed letter also doubles as a record: it proves what terms you communicated and when. If you're using it as a record, skip email entirely and mail it: a single authoritative copy beats two versions that might differ.
One more practical note: address it to a named person, not "Accounts Payable." Named-person mail gets opened faster and filed correctly. And if you included your vendor number or customer account reference anywhere in your other documents, repeat it here so the vendor can match the letter to your account.
Ready to mail it? Send your letter with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it's printed and mailed.
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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