Invoice automation: from 100 manual emails to zero intervention

The challenge

At this accounting firm, vendor invoices all arrived at the same mailbox: over 100 a month. The bookkeeper — a professional with decades of experience but no technical knowledge — spent several hours each week on a fully manual process:

1. Open each email and check whether it contained an invoice.
2. Download the attached PDF.
3. Identify the vendor.
4. File the PDF in the right folder.
5. Mark the email as processed.

Every hour spent on this was an hour not spent on actual accounting work. And there was no way to scale if the volume grew.

The solution

I built a full n8n flow that handles everything automatically:

1. Inbox monitoring: every 5 minutes, the system checks for new emails.
2. Attachment extraction: it identifies PDFs that look like invoices.
3. Rule-based classification: it uses a Google Sheet maintained by the bookkeeper to match each vendor (sender, subject keywords, etc.) to a target folder.
4. Filing: the PDF is saved in the right Google Drive folder with a standardized filename.
5. Logging: every processed invoice is logged in a Sheet with date, vendor and status.

The key insight: the rules live in a Google Sheet the bookkeeper already knows how to use. When a new vendor appears, she adds a row. No developer involvement.

Technical stack

• Orchestration: n8n (self-hosted)
• Sources: Gmail / IMAP
• Storage: Google Drive
• Rules UI: Google Sheets
• Monitoring: n8n error log + Sheet summary

The outcome

Zero manual intervention. The bookkeeper wins back several hours each week to focus on accounting. When a new vendor shows up, she adds a line in the Sheet and the automation picks it up. No code, no tickets.

And if something breaks, an alert reaches my email and I respond as part of the monthly support plan.