Groundhogg Address Verification with n8n & Lob

Ensure the mailing addresses you collect in Groundhogg are valid and deliverable by automating address verification with n8n and Lob. This easy-to-follow workflow validates addresses as soon as a contact is created, tags deliverable or non-deliverable contacts, and notifies your team when manual review is required.

Why verify mailing addresses in your CRM?

Mailing address verification improves deliverability for physical mail campaigns, reduces returned mail and wasted postage, prevents manual-entry typos, and keeps customer data high quality. When address errors are caught early, teams save time and preserve campaign ROI.

Overview of this automation

This n8n workflow listens for a webhook from Groundhogg whenever a new contact is created or updated. It maps address fields, sends a verification request to Lob’s US address verification API, checks the response for deliverability, and then:

Tags the contact in Groundhogg as Mailing Address Deliverable if verified
Tags the contact as Mailing Address NOT Deliverable if not verified
Notifies your operations team via Slack for addresses that require manual review

Prerequisites

n8n instance with web access (or n8n.cloud)
Groundhogg CRM account and ability to send webhooks from funnels or automations
Lob account and API key (see LOB setup below)
Slack webhook or Slack app to notify a channel (optional)

Key nodes in the workflow

CRM Webhook Trigger

This node receives POST payloads from Groundhogg. Configure your Groundhogg funnel or automation to hit the n8n webhook URL and include address fields such as address, address2, city, state, and zip_code.

Set Address Fields

Standardizes and maps incoming fields into the expected names. For example:

{
  "address": "1600 Pennsylvania Avenue NW",
  "address2": "",
  "city": "Washington",
  "state": "DC",
  "zip_code": "20500"
}

Address Verification (Lob)

Calls Lob’s US verifications endpoint https://api.lob.com/v1/us_verifications with the mapped address fields. Lob returns standardized address components and a deliverability field indicating if the address is deliverable.

Deliverability Router

A switch node inspects $json.deliverability. Routes labeled deliverable follow the success path; otherwise they go down the non-deliverable path.

Mark Deliverable / Mark NonDeliverable

These HTTP request nodes call a Groundhogg webhook listener or API to update the contact: add a tag, write a note, start another automation, or update a contact field. Typical actions:

Add tag: Mailing Address Deliverable
Add tag: Mailing Address NOT Deliverable (and trigger a manual verification automation)

Notify Team Slack

When an address is non-deliverable, the workflow can send a Slack message to a channel such as #ops so your team can investigate.

LOB setup

To use Lob for verification:

Create an account at Lob.com
Create an API key (https://help.lob.com/account-management/api-keys)
In n8n, configure the Address Verification HTTP Request node to use Basic Auth with your Lob API key as the username (leave password blank)

Mapping Groundhogg fields

When configuring Groundhogg to send the webhook, include these fields in the payload (field names should match or be mapped in the Set node):

id (contact id)
address
address2
city
state
zip_code
email / phone (optional)

Sample webhook payload from Groundhogg

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

What Lob returns (example)

A successful Lob verification returns address components and metadata. Key fields to check:

deliverability — typically values like deliverable, not deliverable, or unknown
primary_line, city, state, zip_code — standardized values

Example cURL request to Lob (for testing)

curl -u YOUR_LOB_API_KEY: \
  -X POST https://api.lob.com/v1/us_verifications \
  -d primary_line='1600 Pennsylvania Avenue NW' \
  -d city='Washington' \
  -d state='DC' \
  -d zip_code='20500'

Handling deliverability

Decide how your system should respond based on the verification result. Common approaches:

Deliverable: add a verification tag and continue with onboarding sequences
Not deliverable: add a non-deliverable tag, notify ops for manual review, or trigger an automated follow-up that asks the contact to confirm their address
Unknown/Partial: route to a human workflow for deeper investigation

Security and privacy considerations

Protect your Lob API key. Use n8n credential storage or environment variables instead of placing keys directly in HTTP nodes.
Ensure your webhook URLs are not publicly discoverable and validate incoming requests if possible.
Comply with data protection laws (e.g., only store PII that you need, use secure transport HTTPS).

Testing and debugging

Use the n8n pinData or manual trigger to simulate sample payloads.
Check the Address Verification node output to see Lob’s response JSON.
If deliverability values don’t match expected strings, inspect the exact deliverability value and update the Switch node rules accordingly.
Log failures and add retries for transient HTTP errors.

Troubleshooting tips

401 from Lob: verify API key and Basic Auth setup.
Unexpected deliverability values: print the full Lob response and map accordingly.
Groundhogg updates not appearing: confirm the HTTP Request node points to the correct Groundhogg listener URL and the payload includes the contact id.

Extend this workflow

Ideas to expand the automation:

Automatically normalize and write Lob’s standardized address back to the contact record.
Integrate a retry loop for addresses where Lob returns unknown.
Trigger a two-way email or SMS verification flow asking the contact to confirm or correct their address.
Maintain a report/dashboard of verification rates and error counts for ongoing quality monitoring.

Costs and limits

Lob’s API typically charges per verification request. Check your Lob pricing tier and monitor usage. Design batch or sampling strategies if you have high volume to control cost.

Conclusion

Automating address verification between Groundhogg and Lob using n8n reduces manual work, improves mail deliverability, and keeps your CRM data accurate. The template included—webhook trigger, field mapping, Lob verification, deliverability routing, Groundhogg updates, and Slack notifications—provides a practical, production-ready starting point.

Get started

Ready to implement address verification? Deploy this n8n template, connect your Lob API key and Groundhogg webhook, and test with a few sample contacts. If you’d like help customizing the workflow for your team, contact us for a consultation.

Call-to-action: Deploy the template in n8n, run a few test contacts, and tag your ops channel for non-deliverable addresses. Need help? Reach out to our team to tailor this automation for your CRM.

View template →