# Custom integration

## Don't see your tool? We'll build it.

Letterhead connects to 20+ ESPs, CMSs, CRMs, CDPs, and ad servers out of the box — and when your stack has something we don't, we build the connection for you. Most go live in days, not quarters.

## What we connect

### If it has an API, we can wire it to the newsletter.

Letterhead reads content and data in, syncs audiences and engagement both ways, and sends through whatever you already use.

### Any ESP or sending platform

Keep your sender; we wire Letterhead to send through it.

### Any CMS or content source

Pull articles, events, and media into editions automatically.

### Any CRM, CDP, or warehouse

Sync audiences and engagement both ways.

## How it works

### A custom integration, run by a Letterhead lead.

No long enterprise project. We scope the connection with you, build and test it on your data, and ship it — usually in days.

### What we need from you

- The tool and what you want to connect (content in, data sync, or send).
- API access or credentials for a test environment.
- One real newsletter and audience to validate against.

### What we deliver

- A scoped integration plan with a timeline.
- The built connection, tested on your data.
- Native connector, API, or MCP — whatever fits your stack.
- Ongoing support from the Letterhead team.

## Tell us what's in your stack.

Send us the tool you need connected and what you're trying to do. We'll come back with a plan and a timeline — most custom integrations go live in days.