How to Send an Invoice by Email (Without It Being Ignored)
Subject lines that get opened, what to write in the email body, how to name the PDF attachment, and when to follow up.
Email is how most invoices travel, and most invoices that go unpaid were never really seen. A vague subject line, a missing attachment, or an email that lands on a Friday afternoon can add weeks to your wait. Sending an invoice well takes five minutes — here's the whole process.
Name the PDF file properly
Before you attach anything, rename the PDF so it identifies itself: INV-2026-0042-Acme-Corp.pdf. Clients download dozens of attachments; a file named 'invoice.pdf' or 'document(3).pdf' gets lost. Include your invoice number and the client or project name.
Write a subject line that says what it is
The subject should contain three things: the word Invoice, the invoice number, and your business name. 'Invoice INV-2026-0042 from Brightline Studio — due Nov 1' works. Avoid clever or vague subjects like 'Following up' — those get deprioritized or filtered.
Keep the body short and complete
Three to five sentences: a greeting, what the invoice covers, the amount and due date, how to pay, and a thank-you. For example: 'Hi Sara, attached is invoice INV-2026-0042 for the October retainer ($1,200), due November 14. You can pay by bank transfer using the details on the invoice — please use the invoice number as the reference. Thanks!'
Attach the PDF — and double-check it
Attach the file rather than linking to it; links break, and some clients can't open them. Before hitting send, open the attachment once to confirm it's the right invoice and the totals are correct.
Send at the right time
Send on a weekday morning in the client's timezone, ideally Tuesday through Thursday. Invoices sent late on Friday or over the weekend start Monday buried under everything else.
Schedule your follow-up now
Put two reminders in your calendar before you close the tab: a friendly heads-up a few days before the due date, and a nudge the day after it's due. Deciding this now means it actually happens.
If there's no reply
After your first nudge, confirm the basics before assuming the worst: did the email go to the right person (accounts payable, not just your day-to-day contact)? Did it land in spam? A quick 'just checking this reached you' message — or a phone call — resolves most silent invoices.