The short version
Same starting point. Different route after submit.
Basin signs webhooks and has projects and an API, which makes it a close comparison. Postbag keeps every message and sending attempt together, lets an agent run the setup from the free plan, and can run on your own infrastructure.
The evidence
What each service says it does.
These are not ratings. They are the practical details that tend to matter after a Form is live.
| Capability | Postbag | Basin |
|---|---|---|
| Free tier | 5 forms, 1,000 submissions/month, 5 destinations, 90-day retention | 1 form, 50 submissions/month, 30-day retention (Basin pricing) |
| Entry paid | Pro $15/month ($12/month billed yearly); Team $49/month ($39/month billed yearly) | Starter $12.50/month billed yearly |
| Management API | Your agent can create, inspect and manage forms from one API | Forms, submissions, projects, form webhooks (Growth+) |
| Webhooks | Yes; HMAC-signed when a secret is configured, with visible retries | Yes, signed with X-Basin-Signature, Growth+ |
| Yes (Resend), Reply-To from the submission | Yes, plus SMS | |
| Chat destinations | Telegram today; Slack and Discord next | Slack, Discord |
| Spam | Honeypot, rate limits, approved origins and Cloudflare Turnstile; flagged messages stay available to review | reCAPTCHA v2/v3, hCaptcha, Turnstile, honeypot, duplicate/country/burner-email filters |
| File uploads | Not yet (text fields only; 256 KB) | Yes |
| Self-hosting / source | Yes, the same product you use in the cloud | No |
| Keeping fields tidy | Keeps changing field names clear and catches surprises before they spread | Real-time email and phone checks; no tracked history for field rules |
| Many sites, one place | Keep forms from many sites together, then send each one where it belongs | Projects, Agency plan, unlimited collaborators |
| For AI agents | Your agent can set up, test and manage a form without a browser | llms.txt; AI lead features; no MCP or CLI found |
On a small screen, the table scrolls sideways so the full wording stays readable.
Source note Basin facts checked on against: usebasin.com/pricing, API reference, Webhooks (signed). Prices and quotas change, so check the vendor pages before deciding. Tagline quoted: "a lead-capture platform for the web" (Basin's llms.txt).
The practical choice
Both can be the right answer.
Choose Basin if
- You want SMS alerts and lead-qualification features out of the box.
- You need uploads and many captcha options.
Choose Postbag if
- You want webhook signing and an API on the free tier.
- Many forms with different field names should arrive neatly in one place, on a schedule that suits you.
- You need self-hosting or agent-run setup.
What Postbag keeps hold of
The Submission does not disappear into the notification.
Postbag treats a Submission as a database row before anything else and Delivery as an outbox drained by a worker. Each Delivery keeps its retry count and latest outcome, including for spam. Streams let many Forms with different field names map onto one versioned Schema and reach one partner or CRM with windows and digests. Add a secret and Postbag signs each webhook attempt. The same /openapi.json and /llms.txt describe the API an agent uses to create, verify and route a Form without a browser. And it ships as one Docker image plus Postgres, so the hosted product and a self-hosted install are the same thing.
