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.