Retransmit vs Plunk
Plunk folds transactional email, campaigns, and automations into one open source tool with one contact list. Retransmit does one job, transactional delivery, and does it with bigger batches and heavier webhooks.
By the Retransmit team. Last updated .
Retransmit builds one of the products compared here. Every competitor number was checked on the vendor's own site on the date above, and nothing on this page is paid placement.
Plunk's pitch is replacing your email API and your marketing tool at once: workflows, segments, inbound email, a visual editor, and a flat price of $1.00 per 1,000 emails. Retransmit's pitch is owning a focused transactional pipeline: API and SDK sends, 10,000-email batches, per-email event history, and HMAC-signed webhooks, funded by prepaid credits or self-hosted for free. Which one fits depends on whether email is a product surface for you or an infrastructure concern.
At a glance
Both are open source and self-hostable. Plunk optimizes for breadth, Retransmit for the transactional core.
| Retransmit | Plunk | |
|---|---|---|
| Positioning | Transactional email API, cloud or self-hosted | Open source platform for transactional, campaigns, and automations |
| Source code | AGPL-3.0 on GitHub, MIT licensed SDK | AGPL-3.0 on GitHub |
| Self-hosting | Yes, free | Yes, Docker Compose, no per-email cost |
| Cloud hosting | Prepaid credits | EU-hosted, $1.00 per 1,000 emails |
| Free tier | Self-hosted, every feature | 1,000 emails a month with Plunk branding |
| SDKs | Node.js, plus REST | Node.js, plus REST and SMTP |
| Best fit | Backends that send receipts, alerts, and OTPs at volume | Products that want marketing and lifecycle email too |
Sources: Plunk pricing
Pricing
Plunk is refreshingly simple: $1.00 per 1,000 emails, every feature included, unlimited contacts, with an optional monthly spend cap. The free tier covers 1,000 emails a month with Plunk branding on them.
Retransmit is prepaid. Top up a balance, send until it runs out, top up again. No branding on free sends because there is no branded tier; the free option is self-hosting.
| Retransmit | Plunk | |
|---|---|---|
| Free tier | Self-hosted, unbranded, every feature | 1,000 emails a month, Plunk branding |
| Paid price | Prepaid, pay per send | $1.00 per 1,000 emails, all features |
| Contacts | Not stored | Free, unlimited |
| Spend control | Balance runs down, never over | Optional monthly spend cap |
| Payment methods | Bank transfer, mobile money, local currency | Card |
Sources: Plunk pricing
Feature comparison
Plunk's automations are its standout: event-triggered workflows with waits and branches, live segments, and inbound email that turns replies into contacts. Retransmit's standouts are operational: batching, queues with backoff, and a webhook system built like a payments provider's.
| Feature | Retransmit | Plunk |
|---|---|---|
| Transactional API | Yes | Yes |
| Batch sending | Yes, 10,000 per request | Not documented |
| Marketing campaigns | Not yet | Yes, with analytics |
| Automations and workflows | Not yet | Yes, visual canvas |
| Segments | Not yet | Yes, live query-based |
| Inbound email | Not yet | Yes, one MX record |
| Email editor | Not yet | Yes, visual and HTML |
| SMTP relay | Not yet | Yes |
| Webhooks | 9 event types, HMAC-SHA256, 8 retries | Event hooks, inbound POSTs to your endpoints |
| Domain setup | SPF and DKIM records shown in dashboard | DKIM, SPF, DMARC configured automatically |
| Agent tooling | Not yet | MCP server with 23 tools |
Which one should you pick
- Pick Plunk if you want lifecycle email: campaigns, automations, and segments against one contact list.
- Pick Plunk if inbound email or an editor for non-developers matters.
- Pick Retransmit if you send transactional volume from a backend and want batching, queues, and signed webhooks as the core product.
- Pick Retransmit if you want prepaid billing with local payment methods, or the smaller stack to self-host.
If email is infrastructure for you, not marketing, start with the stack that treats it that way.
Related resources
Open source email API comparison
Retransmit, useSend, and Plunk, side by side.
Retransmit vs useSend
The two SES-based open source stacks compared.
Retransmit quickstart
Verify a domain, grab an API key, and send your first email in under five minutes.
Webhook docs
Nine event types, HMAC-SHA256 signatures, and a five line verification example.
Questions people ask
Is Plunk open source?
Yes. Plunk's platform is AGPL-3.0 on GitHub and can be self-hosted with Docker Compose at no per-email cost. Retransmit is AGPL-3.0 too, with an MIT licensed SDK and a smaller footprint to run.
What does Plunk cost?
As of September 1, 2026, Plunk's cloud is $1.00 per 1,000 emails with every feature and unlimited contacts, after a free tier of 1,000 emails a month that carries Plunk branding.
Does Retransmit have automations like Plunk?
No. Retransmit does not have workflows, segments, or campaigns yet. Its webhook events can drive your own automation in your backend, but there is no visual builder.
Which handles high transactional volume better?
Retransmit is built around that case: one request queues up to 10,000 emails, a rate-aware worker drains the queue with retries and backoff, and every message keeps its own id, log, and webhook events. Plunk does not document a batch API.