Groundhogg Address Verification with n8n & Lob

Automatically verify mailing addresses for new contacts in Groundhogg CRM using an n8n workflow and the Lob address verification API. This approach improves deliverability, reduces returned mail, and catches manual-entry typos before you print or mail anything.

Why verify addresses in your CRM?

Invalid or poorly formatted mailing addresses cause wasted postage, failed deliveries, and can negatively affect your engagement metrics. Verifying addresses as contacts are added to Groundhogg ensures your database stays clean and actionable. Key benefits include:

Reduced returned mail and postage waste
Improved campaign deliverability
Better segmentation and personalization
Automated workflows for manual review when needed

High-level workflow

The automation follows a simple flow in n8n:

Receive a webhook from Groundhogg when a new contact is added.
Standardize and set address fields in n8n.
Call the Lob US verifications endpoint to check deliverability.
Route based on the verification result — mark the contact as deliverable or not in Groundhogg.
Notify your ops team (example: Slack) for manual verification of non-deliverable addresses.

n8n workflow explained (nodes)

1) CRM Webhook Trigger

Expose a POST webhook in n8n that Groundhogg calls when a new contact is created. Include the address fields in the webhook payload (address, address2, city, state, zip_code, id).

2) Set Address Fields

Use the Set node to normalize and map the incoming JSON fields to the names you want to send to Lob. This makes it easy to support multiple CRMs later by only adjusting the mapping.

3) Address Verification (HTTP Request)

Send a POST to Lob’s US verifications endpoint (https://api.lob.com/v1/us_verifications) with the normalized address fields. Lob responds with a deliverability field you can use to route the contact.

4) Deliverability Router (Switch)

Use a Switch node to evaluate the Lob response. If deliverability === “deliverable”, mark the contact as verified in Groundhogg. If not, mark it non-deliverable and trigger internal processes.

5) Mark Deliverable / Mark NonDeliverable

Use HTTP Request nodes to POST back to Groundhogg (or call a Groundhogg funnel webhook) to add tags, update a field, add a note, or start another automation. For non-deliverable addresses, also send a Slack message or create a task for your ops team.

Step-by-step setup

1) Create a Lob account and API key

Sign up at Lob.com and generate an API key (Account > API Keys). In n8n, configure the HTTP Request node to use Basic Auth with your Lob API key as the username and an empty password, or pass the key via an Authorization header as documented by Lob.

2) Configure the Groundhogg webhook

In Groundhogg, create an automation or funnel that triggers a webhook whenever a new contact is added or when a contact’s mailing address changes. Point that webhook to the n8n webhook URL (the path shown in the CRM Webhook Trigger node).

3) Map fields in the Set node

Use a Set node to map incoming fields to the names Lob expects. Example assignments:

{
  "primary_line": "1600 Pennsylvania Avenue NW",
  "secondary_line": "",
  "city": "Washington",
  "state": "DC",
  "zip_code": "20500"
}

4) Call Lob’s US verification endpoint

Configure an HTTP Request node in n8n to POST to:

https://api.lob.com/v1/us_verifications

Include the address payload in body parameters. Lob returns JSON that includes a deliverability field you can use to route the next steps.

5) Route and update Groundhogg

Use the Switch node to check $json.deliverability. Typical outcomes:

deliverable — add tag “Mailing Address Deliverable” to the contact, update a custom field, or start a follow-up automation.
not deliverable — add tag “Mailing Address NOT Deliverable”, start a manual verification automation, and notify Slack.

Example webhook payload from Groundhogg

{
  "id": "5551212",
  "email": "mr.president@example.com",
  "address": "1600 Pennsylvania Avenue NW",
  "address2": "",
  "city": "Washington",
  "state": "DC",
  "zip_code": "20500",
  "phone": "877-555-1212"
}

Best practices

Rate-limit API calls and handle Lob quotas gracefully.
Store verification status and raw response in the contact record for auditing.
Use tags to trigger secondary automations (e.g., manual verification, contact outreach).
Sanitize and trim address fields before sending to the verification API.
Log errors to a centralized monitoring channel (Slack, email, or error queue).

Troubleshooting

Common issues

If you get unexpected responses from Lob, verify that the address fields are mapped correctly and that you are using the correct API key and Basic Auth configuration. If the Lob response is missing deliverability, log the full response for diagnosis.

Testing the flow

Use the pinData feature in n8n to simulate incoming webhook payloads. Test both clearly valid addresses and intentionally bad addresses to ensure both branches of the router behave as expected.

Security and compliance

Do not hard-code API keys into shared flows or public repositories. Use n8n credentials or environment variables to keep secrets secure. If you store address data, ensure you comply with applicable privacy laws and your organization’s data retention policies.

Wrap-up and next steps

Adding address verification to your Groundhogg workflows with n8n and Lob is an efficient way to maintain a high-quality contact database and reduce failed mailings. The pattern is flexible — you can swap Lob for another verification provider or add more logic for international addresses.

Call to action

Ready to set this up? Download the n8n workflow template, create your Lob API key, and connect your Groundhogg webhook. If you’d like help customizing the flow for international addresses or adding more complex automations, contact our team or subscribe for workflow templates and tutorials.

View template →