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Automated Invoice Mailing

This guide shows how to automatically send printed invoices via the Intelliprint hybrid mail API whenever invoices are created or become overdue. It is ideal for:
  • Accounting and billing platforms
  • Subscription and SaaS systems
  • Finance teams replacing manual invoice printing

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Overview

High-level flow: You can implement automated invoice mailing using:
  • HTML-based letters (for simple layouts)
  • PDF-based letters (for existing invoice PDFs)
  • Backgrounds and templates for consistent branding

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Step 1: Decide HTML vs PDF

Option A – HTML invoices Option B – PDF invoices In both cases, you pass customer address data and invoice details to Intelliprint.

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Step 2: Map Invoice Events to Postal Actions

Decide when to send printed invoices. Common patterns:
  • Initial invoice generation
    • Every time an invoice is created for customers with postal preferences.
  • Overdue reminders
    • Send a letter if an invoice has not been paid X days after due date.
  • Final notice
    • Send a tracked or recorded letter before escalation.
You can control this using your own business logic in your billing system or integration service.

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Step 3: Implement the API Call

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Example: HTML-based invoice letter (Node.js)

import Intelliprint from "intelliprint";

const ip = Intelliprint(process.env.INTELLIPRINT_API_KEY);

export async function sendInvoiceByPost(invoice, customer) {
  const html = `
    <h1>Invoice ${invoice.number}</h1>
    <p>Dear ${customer.name},</p>
    <p>Thank you for your business. Your invoice is now due on <strong>${invoice.due_date}</strong>.</p>
    <p>Amount due: <strong>£${invoice.amount_gbp.toFixed(2)}</strong></p>
    <p>You can also pay online using your usual method.</p>
    <p>Kind regards,<br>${invoice.company_name}</p>
  `;

  const printJob = await ip.prints.create({
    testmode: true, // start in test mode
    content: html,
    recipients: [
      {
        address: {
          name: customer.name,
          line: customer.postal_address.line,
          postcode: customer.postal_address.postcode,
          country: customer.postal_address.country || "GB"
        }
      }
    ],
    metadata: {
      invoice_id: invoice.id,
      customer_id: customer.id,
      channel: "invoice_post"
    },
    confirmed: true
  });

  await db.invoices.update(invoice.id, {
    postal_print_job_id: printJob.id
  });
}
Switch testmode to false once you have tested the flow.

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Example: PDF-based invoice letter (Node.js)

import Intelliprint from "intelliprint";
import fs from "fs";

const ip = Intelliprint(process.env.INTELLIPRINT_API_KEY);

export async function sendInvoicePdfByPost(invoice, customer) {
  const pdfPath = `/tmp/invoices/${invoice.id}.pdf`; // generated earlier in your system

  const printJob = await ip.prints.create({
    testmode: true,
    file: fs.createReadStream(pdfPath),
    printing: {
      double_sided: "yes"
    },
    recipients: [
      {
        address: {
          name: customer.name,
          line: customer.postal_address.line,
          postcode: customer.postal_address.postcode,
          country: customer.postal_address.country || "GB"
        }
      }
    ],
    metadata: {
      invoice_id: invoice.id,
      customer_id: customer.id,
      channel: "invoice_post"
    },
    confirmed: true
  });

  await db.invoices.update(invoice.id, {
    postal_print_job_id: printJob.id
  });
}

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Step 4: Track Statuses and Build an Audit Trail

For finance and compliance, you should store:
  • Intelliprint print_job_id
  • Letter statuses and key timestamps
  • Any returned or failed mail indicators
Use Track, Retrieve & Cancel to:
  • Retrieve print jobs and letters by ID
  • Check status (e.g. waiting_to_print, printing, sent, returned)
  • Cancel jobs that have not yet been printed
Augment this with Webhooks to push status updates back into your billing system automatically.

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Step 5: Control Costs & Service Levels

Invoices can be time-sensitive and high volume. Use:
  • Postage choices and scheduling
    See Postage & Scheduling to choose between first class, second class, tracked services and dispatch dates.
  • Double-sided printing
    Enable double-sided printing for multi-page invoices to reduce sheet count and costs. See Double-Sided Printing in the HTML quickstart.
  • Test mode for cost estimation
    Use testmode: true with your real data to calculate actual per-invoice and per-campaign costs without sending live mail. See Understand Costs.

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Example: Daily Invoice Batch

You can also run a daily job to send any outstanding invoices: 
async function runDailyInvoiceBatch() {
  const invoicesToSend = await db.invoices.findAll({
    where: {
      delivery_method: "post",
      posted_via_intelliprint: false,
      status: "open"
    }
  });

  for (const invoice of invoicesToSend) {
    const customer = await db.customers.findById(invoice.customer_id);
    await sendInvoicePdfByPost(invoice, customer);
  }

  console.log(`Queued ${invoicesToSend.length} invoices for postal mailing`);
}

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Next Steps

PDF + Split Quickstart

Learn how to send invoices from PDFs

Backgrounds & Letterheads

Add branded invoice letterheads

Track, Retrieve & Cancel

Build an audit trail for posted invoices

Understand Costs

Estimate postal invoice costs at scale