The direct mail API your engineers will actually use.
Trigger postcards, letters, and handwritten notes off any product event. REST API, webhooks, idempotency keys, and an MCP server so your AI agents can send physical mail autonomously. Built for SaaS and technology teams that ship every day.
Capabilities
Built for teams that prefer JSON over PDFs.
- REST API and webhooks
- Send one piece or one million through the same JSON endpoint. Idempotency keys, webhook callbacks on every status, and SDK-friendly responses.
- MCP server for AI agents
- Connect MailStream to Claude, GPT, or any compatible agent. Let it decide when a postcard or handwritten note is the right move, autonomously.
- Product-event triggered sends
- Fire mail off any product event: trial start, feature adoption, churn risk score, milestone hit. Wire it once, run it forever.
- Handwritten notes via API
- Real-pen handwritten notes generated through robotic writing arms. Trigger one with the same call you would use for a postcard.
- Webhook delivery confirmations
- Every printed, mailed, scanned, and delivered status posted back to your webhook. Close the loop in your warehouse or BI stack.
- SOC-friendly, HITRUST-certified
- Production inside a HITRUST-certified facility. Encryption end to end, audit logs, and security review documentation ready for procurement.
- 12
- MCP tools for AI agents
- 24hr
- Print-to-ship turnaround
- 5min
- First-postcard onboarding
- 99.9%
- API uptime
- API-first by default
- JSON in, JSON out. Idempotency keys, webhook callbacks, and SDK-friendly responses on every endpoint.
- MCP server for agents
- The first direct mail platform with a Model Context Protocol server. Plug Claude or GPT in and let it send mail.
- HITRUST-certified
- Production runs inside a HITRUST-certified facility. SOC-friendly access controls and security review docs ready.
- 25+ years of expertise
- Twenty-five years of direct mail at scale, packaged behind a modern API. We bring the print floor. You bring the trigger.
Use cases
From trial signup to churn save, fired off product events.
- Trial-end save
- Trigger a personalized postcard 3 days before a trial ends. A different channel breaks through inbox fatigue and recaptures the at-risk cohort.
- Milestone celebrations
- Send a handwritten note when a customer hits their first 1K MAU, ships their 100th deploy, or closes their tenth invoice. Loyalty earned in pen.
- Churn rescue
- Fire a save mailer at the first churn signal. Reach users who have already unsubscribed from email or disabled product notifications.
- Account-based marketing
- Drop branded packages on target accounts the day they enter your ICP fit threshold. Coordinated with outbound, paid, and SDR motion.
- Onboarding kits
- Welcome new customers with a branded kit on signup. Stickers, a swag piece, and a real handwritten note. Triggered straight from your sign-up flow.
- Autonomous AI agent sends
- Let an agent decide when to send. MailStream is the first direct mail platform with an MCP server, so any compatible model can send physical mail.
What everyone is saying
Trusted by engineering and growth teams.
We hooked MailStream into our churn-risk webhook and run a save mailer 48 hours before predicted cancellation. Net retention is up double digits since.
Ethan K.
Engineering Lead, Lattice Health
The MCP server is the killer feature. Our agent decides when a customer earned a handwritten note and ships it autonomously. We did not believe direct mail could be this engineer-friendly.
Riley S.
Head of Growth, Forge Analytics
We integrated the API in one day. Onboarding kits ship the same hour the customer signs up. Our trial-to-paid lifted measurably in the first month.
Mia R.
VP of Product, Beacon Cloud
Engineering, growth, lifecycle, and ABM teams use MailStream to add a physical channel to their product stack without managing print vendors or PDF templates.