How to Send an Invoice: Email, Mail, and Portal Delivery Methods
Creating an invoice is only half the process. The other half is getting it to the right person at the right time in a format they can process. This guide covers the three main delivery methods for invoices, when to use each one, and how to confirm the invoice was received.
What information does an invoice need before sending?
Before sending an invoice, confirm that all required fields are filled in correctly: the seller and buyer contact details, invoice number and date, itemized goods or services with quantities and rates, the total amount due, and payment instructions. Each field should be reviewed for typos, especially the payment details where a single wrong digit can delay a bank transfer by weeks.
The invoice format matters too. PDF is the standard because it preserves the layout across all devices. Sending an editable format like Excel or Word risks the recipient accidentally modifying the document. For guidance on what each field should contain, refer to the small business invoicing guide.
File size is another consideration. High-resolution logos or embedded images can make a PDF too large for email attachments. Most email servers cap attachments at 10 MB to 25 MB. If the invoice exceeds that, upload it to a secure link and include the link in the email body.
How to send an invoice by email?
Email is the most common method for sending invoices. It is fast, free, and provides a written record of when the invoice was sent. Attach the invoice as a PDF and write a short email that includes the invoice number, the amount due, the due date, and a brief message. The attachment should be named clearly, such as "Invoice-2026-001-YourCompany.pdf".
The subject line should include the invoice number and the word "Invoice" so the client can find it later. For example: "Invoice INV-2026-001 from Your Company". The body should be concise. Include the invoice amount and due date in the email text so the client does not need to open the attachment to see the basics.
For best results, send the invoice to a specific person rather than a general accounts email address. If the client has a dedicated accounts payable team, confirm the correct contact and any special requirements they have for invoice submission. Some large companies require invoices to be submitted through a vendor portal rather than by email.
For ready-to-use email wording, see the invoice email templates guide. It includes templates for first-time invoices, recurring invoices, and payment reminders.
When to send an invoice after completing work?
Send the invoice immediately after the work is completed or at the end of the agreed billing cycle. Waiting longer than necessary extends the payment timeline and increases the risk of the client forgetting the details of the project. The general rule is: the sooner the invoice is sent, the sooner payment arrives.
For fixed-price projects, send the invoice on the day of delivery. For hourly or time-based work, send the invoice at the end of each week or month depending on the agreement. For retainer arrangements, send the invoice at the beginning of the billing period so payment arrives before the next period starts. Milestone-based projects should trigger an invoice at each milestone completion.
The invoice date matters because it determines the due date. If the invoice is dated July 1 with Net 30 terms, payment is due July 31. If the invoice is created on July 1 but not sent until July 15, the client still has until July 31 under most interpretations, but this can cause confusion. Date the invoice with the actual send date, not the completion date.
What to do if a client says they never received the invoice?
If a client claims they did not receive the invoice, the first step is to confirm the correct email address. A typo in the recipient address is a common cause of lost invoices. Resend the invoice and ask the client to confirm receipt. If the email bounces, check for other contact methods or ask the client for an alternative address.
Spam filters can also intercept invoice emails. Words like "invoice", "payment", and "bank details" in the subject line sometimes trigger spam filters. Ask the client to check their spam folder. For future invoices, consider asking the client to whitelist the sender email address. Using a professional email domain rather than a free email provider also helps with deliverability.
If email continues to be unreliable, switch to a client portal or a shared drive where invoices can be uploaded and the client can download them on demand. Some invoicing tools include automatic download links in the email body, which reduces the chance of attachment filtering.
How to track whether an invoice has been paid?
Tracking invoice payments requires a system for matching outgoing invoices to incoming payments. The simplest method is to check the bank account regularly and match deposits to invoice numbers. For businesses with many transactions, accounting software can automate this by syncing with the bank feed and flagging unpaid invoices.
For manual tracking, maintain a spreadsheet with columns for invoice number, client name, amount, date sent, due date, and payment status. Update the status when payment is confirmed. This provides an at-a-glance view of outstanding invoices and helps prioritize follow-ups.
Follow up on any invoice that remains unpaid past its due date. Start with a polite reminder, then escalate if needed. For the exact timing and wording of follow-up messages, see the late payment follow-up guide.