BYOSMTP email API

Keep your SMTP.
Add templates, API, and logs.

Connect Gmail, Amazon SES, Zoho, or your own server. Send transactional email through a REST API - without switching providers or paying per email.

Start free Read docs →

Start free during launch - then from $1/month

curl -X POST https://api.letterstack.dev/v1/emails/send \
  -H "Authorization: Bearer ls_live_xxxxx" \
  -H "Content-Type: application/json" \
  -d '{
    "template": "welcome-email",
    "to": "[email protected]",
    "variables": { "name": "John" }
  }'

The problem

Sound familiar?

Free tiers cap you when users show up.

Many transactional email APIs limit free plans to low daily volume. Fine for a demo - painful when signups turn real.

Already have SES, Gmail, or a VPS with SMTP?

You already have delivery. You need templates, a send API, and logs on top - without paying again for managed SMTP you do not need.

Tired of wiring up nodemailer in every project?

Handlebars templates, one POST endpoint, and a dashboard - without rebuilding the same email stack for each side project.

How it works

Up and running in three steps

Connect your SMTP

Any SMTP server works. Gmail, Amazon SES, Zoho, your VPS - just enter host, port, and credentials. We test the connection on save.

Create templates

Build Handlebars HTML templates in the dashboard or via API. Preview them with sample data before you send.

Send via API

One POST request. Pass your template slug and variables. We render the template, send through your SMTP, and log the result.

Features

Templates, API, and logs on your SMTP

Bring Your Own SMTP Any SMTP server - Gmail, Amazon SES, Zoho, self-hosted. If it has a host, port, and credentials, it works.
Handlebars Templates Create, edit, and preview dynamic email templates. Variables, conditionals, loops - full Handlebars support.
REST API One POST to send. Full CRUD for templates. curl works.
Send Logs See queued, sending, sent, and failed - with SMTP error details.
Project Isolation Separate SMTP configs, templates, and API keys per project. Keep staging and production cleanly apart.
Encrypted Credentials SMTP passwords encrypted at rest with AES-256. Your credentials are never stored in plain text.

FAQ

Frequently asked questions

What SMTP servers are supported?

Any SMTP server works - Gmail, Amazon SES, Zoho, Mailgun SMTP, your own VPS running Postfix, or any other SMTP-compatible service. All you need is a host, port, username, and password.

How does pricing work if I bring my own SMTP?

LetterStack charges for the platform - templates, API access, project management, and logs. Since you bring your own SMTP, you're already paying for email delivery (or using a free tier). We don't charge per email.

Is my SMTP password stored securely?

Yes. SMTP credentials are encrypted at rest using AES-256 before being stored. They are never logged, never returned by the API after saving, and only decrypted at send time.

Can I use Gmail for testing?

Yes. Gmail works well for low-volume testing. Use an app password (not your account password). Step-by-step setup is on the blog. For production, use Amazon SES or a similar service.

What happens if my SMTP server is down?

LetterStack queues the send and retries up to three times (with 1s, 5s, and 15s backoff) before marking the email as failed in your send logs. Persistent SMTP outages will still surface as failures after retries are exhausted.

Do you track opens and clicks?

Not yet. Open and click tracking is on the roadmap. Currently, send logs record whether the email was accepted by your SMTP server, which means it was delivered to the outbound queue - not necessarily opened by the recipient.

Can I use multiple SMTP servers per project?

Yes. Each project can have multiple SMTP configs identified by a slug (e.g. production, staging). One config is the default; pass smtp in POST /v1/emails/send to override. Limits: Hobby 1, Starter 2, Pro unlimited.

Connect your SMTP in 5 minutes

First month free. Unlimited email volume. 14-day refund if it’s not for you.

Start free

Keep your SMTP. Add templates, API, and logs.