Head to head
SendHeronvs
Plunk
SendHeron vs Plunk
An open-source email platform you can run yourself, priced per email with unlimited contacts, against a hosted lifecycle tool priced on contact tiers with the sends inside. Both keep contact data in the EU. One drafts your suite and includes 50,000 emails for €19; the other hands you the source and charges a tenth of a cent a send. Here is where each one wins.
Plunk's prices are as of September 22, 2026, from its own pricing page.
Quick comparison
| At a glance | SendHeron | Plunk |
|---|---|---|
| Best for | SaaS teams that want the lifecycle suite drafted, sends included in the tier, and contact data in the EU | Developers and indie SaaS that want the lowest per-email price, unlimited contacts, or their own hosted instance |
| Starting price | €19/mo (Starter, 10,000 contacts, 50,000 emails a month) | $0.001 per email, no base fee; free to 1,000 emails a month |
| Billed on | Subscribed contacts, with a pooled monthly send allowance | Emails sent; contacts unlimited |
| Free plan or trial | 7-day free trial, 1,000 contacts and 5,000 sends, card at checkout | Free to 1,000 emails a month with Plunk branding; self-hosting is free |
| Data residency | EU company; contact data stored in Germany | EU-hosted and GDPR compliant, per its site; self-hosted runs wherever you put it |
Lifecycle automation
Both run event-triggered sequences with delays, conditions and branches. The difference is the starting point: Plunk's builder starts empty, SendHeron's setup starts from a drafted suite.
| Feature | SendHeron | Plunk |
|---|---|---|
| Visual sequence builder with delays and branches | Yes | Event-triggered sequences with delays, conditions and branching |
| A lifecycle suite drafted from your website at setup | Yes, as drafts you approve | Not listed among its features |
| Conditions with AND and OR over tags and properties | Yes | Conditions and branching on contact data |
| Per-step statistics on a sequence | Yes | Opens, clicks, bounces and unsubscribes |
| Dynamic segments | Rules over tags and properties | Segments on behaviour, attributes and engagement |
Sending and deliverability
Plunk meters every send and never caps them; SendHeron includes a pool in each tier. Which is cheaper depends entirely on how busy your list is, and the pricing table below shows both cases.
| Feature | SendHeron | Plunk |
|---|---|---|
| Transactional and marketing from one account | Yes | Yes |
| Send allowance | Pooled monthly allowance per tier: 50,000 emails on Starter | Metered at $0.001 an email, no cap; 1,000 a month on Free |
| Transactional keeps flowing past the allowance | Yes, up to 10% over the pool | Not applicable; a spend cap you set instead |
| SPF, DKIM and DMARC per sending domain | Yes | Set up automatically on custom domains |
| SMTP relay | Not in the API reference | Yes |
| Inbound email | Not in the API reference | Inbound processing with webhooks |
| Free DNS checkers, no account needed | SPF, DKIM, DMARC, deliverability test | SPF, DMARC and DKIM checkers |
Source, hosting and residency
This is the table Plunk wins outright, and it is here in full. If the source or self-hosting is your requirement, SendHeron is not a candidate.
| Feature | SendHeron | Plunk |
|---|---|---|
| Open source | no | AGPL-3.0 |
| Self-hosting | no | Docker Compose, your own infrastructure |
| Where contact data is stored | Germany; EU company | EU-hosted, per its site; self-hosted, wherever you run it |
| Published sub-processor list and DPA on request | Yes | DPA listed in the footer |
API and templates
| Feature | SendHeron | Plunk |
|---|---|---|
| REST API on every tier | Yes | REST API, every plan |
| Official SDKs | Node, with typed send outcomes | Node.js and Python |
| Block editor, no HTML required | Yes | Email editor |
| Tooling for AI agents | Scoped tokens and a plain REST surface | An MCP server page on its site |
Plans and billing
| Feature | SendHeron | Plunk |
|---|---|---|
| Free plan | no | 1,000 emails a month, with branding; self-hosting free |
| Trial | 7 days, 1,000 contacts and 5,000 sends, card at checkout | Not needed; the free plan is the trial |
| What is billed | Subscribed contacts; unsubscribed and bounced stored free | Emails sent; contacts free |
| Spend control | Tier ceilings; transactional grace of 10% past the pool | A monthly spend cap you set |
| Largest published tier | 200,000 contacts (Max, €179/mo) | No ceiling; $0.001 an email at any volume |
| Billing period | Monthly | Monthly |
Pricing comparison
The two models point in opposite directions, so the table shows both directions: three scenarios where the list is busy, and one where it is large and quiet. Plunk's figures are its published $0.001 rate multiplied out.
| Scenario | SendHeron | Plunk |
|---|---|---|
| 5,000 contacts, 25,000 emails a month | €19/mo (Starter) | $25/mo |
| 10,000 contacts, 50,000 emails a month | €19/mo (Starter, at its ceiling) | $50/mo |
| 40,000 contacts, 150,000 emails a month | €49/mo (Growth) | $150/mo |
| 100,000 contacts, 20,000 emails a month (a large, quiet list) | €99/mo (Scale) | $20/mo |
SendHeron prices in EUR, VAT included where it applies; Plunk in USD. Both on monthly billing. The crossover is around 20,000 emails a month, depending on the exchange rate: below it Plunk's meter is cheaper than Starter, above it Starter's included pool is cheaper than the meter. Self-hosted Plunk is free at any size and pays only for its own server and sending provider.
Strengths at a glance
Where Plunk wins
- 01The source. AGPL-3.0, on GitHub, deployable with Docker Compose. You can read it, fork it and run it, and the day you want the data and the sending under your own roof you can have them. SendHeron is closed source and hosted.
- 02Self-hosting is free at any size. No licence, no per-email cost, your own server and sending provider. SendHeron's largest tier is 200,000 contacts and it cannot be self-hosted.
- 03Unlimited contacts. A 100,000-contact list costs nothing to store; only the sends count. SendHeron bills subscribed contacts by tier.
- 04A permanent free plan. 1,000 emails a month, every feature, no card. SendHeron has a 7-day trial.
- 05The cheapest option for a quiet list. A 100,000-contact list that mails once a month is $100 on Plunk and €99 on SendHeron Scale; the same list mailing once a quarter is about $33 a month on Plunk and still €99 on SendHeron.
- 06A spend cap you set. A runaway automation on the hosted plan stops at the number you chose.
- 07SMTP relay and inbound email with webhooks. Neither is in SendHeron's API reference.
Where SendHeron wins
- 01The suite is drafted, and a person approves it. Paste a website URL and the setup proposes the tag schema and drafts welcome, trial, win-back and cancel-save as sequences with real branches. Nothing activates until you switch it on. Plunk's builder starts empty.
- 02The sends are inside the tier. Starter is €19 a month with 50,000 emails included, which is $50 of Plunk sending; Growth is €49 with 150,000, which is $150. A lifecycle suite that actually runs sends more than people budget for.
- 03One allowance, and transactional never stops. Marketing and receipts share one pool, one reputation and one suppression list; a hard bounce blocks every stream, an unsubscribe blocks marketing only for the brand it was given to, and transactional mail keeps flowing up to 10 percent past a spent pool.
- 04Scoped keys. 12 scopes, so a key that reads contacts cannot send, with published per-key and per-organisation rate limits. Plunk's key scoping was not readable from its site.
- 05A typed Node SDK. Send outcomes are typed, so a suppressed address and a transport failure are different branches in your code, and retries and idempotency are on by default.
- 06Several products, one subscription. A workspace per product with its own contacts, tags, sequences, templates, sending domains and keys; unsubscribes per project, bounces account-wide.
- 07A published sub-processor list, a DPA on request, and a company you can name. The residency page says what can be proven and what cannot.
Which tool is right for you?
Choose Plunk if:
- You want the source, or you want to run it yourself
- Your list is large and your sending is light, so the meter is the cheaper model
- You send under about 20,000 emails a month and would rather pay a tenth of a cent each than €19
- You need SMTP relay or inbound email
- You want a permanent free plan rather than a trial
Choose SendHeron if:
- Your lifecycle suite is unbuilt and you would rather approve drafts than design from scratch
- Your list is busy: past about 20,000 emails a month, Starter's included pool beats the meter
- You want a key that can read contacts without being able to send, and rate limits you can read
- You run several products and want one subscription with a workspace each
- You want a vendor with a published sub-processor list, a DPA and onboarding help
Switching from Plunk to SendHeron
Export your contacts from Plunk, then upsert each one over SendHeron's API with the tags your sequences will trigger on; the Node SDK wraps the calls and the API reference states the rate limits to pace against. Plunk's events become SendHeron tags or tracked events, whichever your sequences branch on. If you self-host, the export is a database query and nothing has to be requested from anyone.
Load your unsubscribes as suppressions before anything sends; a suppressed address is refused at send time with a stable reason you can read back. Templates paste in as HTML and you can keep them as HTML or rebuild them in the block builder. Transactional sends move to the send-template endpoint, which the SDK wraps with typed outcomes; anything you were sending over SMTP has to move to the API, because SendHeron has no relay.
Automations are rebuilt, because the two tools model branching differently. Paste your website URL, edit the proposed tag schema, and read the drafted suite before you activate anything; we help map your Plunk workflows onto it during onboarding. If you self-host today, keep the instance running through the trial and cut over one sequence at a time.
Weighing more than these two?See every Plunk alternative
Frequently asked questions
Learn more
- The REST API, scopes and rate limits
- Transactional and marketing on one account
- Templates: blocks or HTML, compiled on the server
- The Node SDK
- The API reference
- GDPR, data residency and the sub-processor list
- Loops vs Customer.io for SaaS
- SendHeron pricing, with the competitor comparison
- How the visual sequence builder works
- Tags and segments
- EU data residency, and what we can and cannot prove
Compare other platforms
The same figures, from another vendor's side.
- AlternativesLoops alternatives10 tools compared at 5,000 contacts.
- AlternativesCustomer.io alternatives10 tools compared at 5,000 contacts.
- AlternativesPlunk alternatives10 tools compared at 5,000 contacts.
- AlternativesSequenzy alternatives10 tools compared at 5,000 contacts.
- Head to headSendHeron vs LoopsSendHeron vs Loops at 5,000 and 10,000 contacts: €19 a month on SendHeron Starter against $49 and $99 on Loops, with feature tables and where each one wins.
- Head to headSendHeron vs Customer.ioSendHeron vs Customer.io at 5,000 and 10,000 contacts: €19 a month on SendHeron Starter against $100 and about $145 on Customer.io Essentials, with feature tables and where each one wins.
- BlogLoops vs Customer.io for SaaSA longer read from the SendHeron blog.
- Every comparison, in one place/alternatives
Plunk's name and logo are trademarks of its owner, shown to identify the product compared. Live pricing drifts, so confirm on the vendor's site before you commit.