Most invoices today arrive by email — and the email matters almost as much as the invoice. A clear subject line, the right recipient and a short, specific message get invoices into the payment queue faster. This guide covers the mechanics and gives you templates to copy.
The essentials
| Element | Best practice |
|---|---|
| Format | PDF attachment (not an editable Word or spreadsheet file) |
| Filename | INV-2026-0047_YourBusiness.pdf |
| Recipient | The person or address that processes invoices (often accounts payable), plus your project contact |
| Subject line | Invoice number, amount, due date — and the client’s PO number if they use one |
| Body | 3–5 sentences: what it’s for, amount, due date, how to pay, thanks |
| Timing | The day the work or milestone is delivered |
Subject lines that work
The subject line should let someone process the invoice without opening it:
Invoice INV-2026-0047 — €1,850.00 — due 14 Nov 2026Invoice INV-2026-0047 for PO 7781 — Northwind Coffee — due 14 NovDeposit invoice INV-2026-0040 — Website project — due on receipt
Avoid “Invoice attached” or “Quick thing” — they get lost in busy inboxes and can’t be searched.
Who to send it to
Ask at the start of every client relationship: “Who should invoices go to, and do you need anything on them?” Many companies have a dedicated accounts payable address and won’t process invoices sent only to the project manager. When in doubt, send to accounts payable and CC your day-to-day contact so they can approve it.
Attach a PDF — or link to one?
- Attach the PDF for most clients. It’s self-contained, works with every email system and can be forwarded to the accounts team intact.
- Links to an online invoice are convenient when they include a payment button, but some corporate systems strip links or require a document for their records — so attach a PDF as well if you can.
- Never send an editable file as the final invoice.
Create the PDF in the invoice generator, then attach it to your email. BillKit runs in your browser and doesn’t send emails for you, so you stay in control of what goes where.
Copy-paste email templates
1. Standard invoice
Subject: Invoice INV-2026-0047 — €1,850.00 — due 14 Nov 2026
Hi Priya,
Please find attached invoice INV-2026-0047 for €1,850.00 for the October content work (4 articles and the newsletter). Payment is due by 14 November 2026.
Bank details are on the invoice; please use INV-2026-0047 as the payment reference.
Thanks — it’s been a pleasure working on this. Daniel
2. First invoice to a new client
Subject: Invoice INV-2026-0051 — Logo project — due 21 Nov 2026
Hi Sam,
Attached is my first invoice for the logo project (INV-2026-0051, $1,350.00), due 21 November 2026.
As it’s our first invoice together, could you let me know if your team needs anything else to process it — a PO number, a supplier form or a different billing address? I’m happy to update it.
Best, Alex
3. Deposit invoice
Subject: Deposit invoice INV-2026-0040 — Website project — due on receipt
Hi Jordan,
Thanks for approving the quote. Attached is the 40% deposit invoice (INV-2026-0040, €4,840.00 incl. VAT). Once it’s received, I’ll confirm the start date — currently pencilled in for 10 November.
Best regards, Mia
See deposit invoices for how to structure these.
4. Milestone or recurring invoice
Subject: Invoice INV-2026-0118 — November retainer — due 8 Nov 2026
Hi Chris,
Here’s the invoice for the November retainer (INV-2026-0118, £2,760.00 incl. VAT), due 8 November. It also includes the 3 additional hours approved in October.
October summary: 20 retainer hours + 3 approved extra hours; delivered 4 blog posts, the newsletter and the monthly report.
Thanks, Sophie
5. Corrected invoice
Subject: Corrected invoice INV-2026-0066 (replaces INV-2026-0061) — Northwind Coffee Ltd
Hi Priya,
As discussed, INV-2026-0061 was addressed to the wrong entity. I’ve attached credit note CN-2026-0005 cancelling it, and a new invoice INV-2026-0066 addressed to Northwind Coffee Ltd. The amount and due date are unchanged.
Apologies for the extra step. Daniel
Corrections should use a credit note, not an edited original.
6. Invoice with a payment link
Subject: Invoice INV-2026-0072 — $480.00 — due 15 Nov 2026
Hi Taylor,
Attached is invoice INV-2026-0072 for $480.00 (October lawn care). You can pay by card at [your payment link] or by bank transfer using the details on the invoice.
Thank you! Jamie
Before you hit send: checklist
- PDF attached and opens correctly
- Filename includes invoice number
- Sent to accounts payable (and CC your contact)
- Subject has invoice number, amount and due date
- PO number included if the client uses POs
- Amount and due date in the email match the invoice
- Payment details are on the invoice
- You’ve logged the invoice and due date in your tracker
After sending
- Ask for confirmation on first invoices: “Could you confirm it’s been received?”
- Diary the due date and a reminder a few days before it for new clients.
- Follow up promptly if it’s late — our late payment reminder templates continue where these leave off.
Email security tips
Invoice fraud often works by impersonating suppliers and changing bank details. Protect your clients and yourself:
- Keep your bank details consistent; if they ever change, tell clients by phone as well as email.
- Encourage clients to verify any change of bank details through a known phone number.
- Don’t send invoices from personal or shared accounts that others can access.
- Be wary of “please resend with new bank details” emails that claim to come from clients or colleagues.
Is emailing an invoice legally valid?
In most countries, invoices sent by email as PDFs are accepted, sometimes subject to the customer’s agreement. Some countries now require structured e-invoices for certain B2B transactions instead of PDFs — see what is an e-invoice. This is general information, not legal advice.