Nitrosend vs Plunk.

Campaigns, flows, and transactional email, run by an agent instead of a dashboard.

TL;DR

Plunk is an open-source email platform under AGPL-3.0 that puts transactional sending, campaigns, and workflow automation in one product. Run it yourself on Docker, or take the hosted plan at a flat $0.001 an email with unlimited contacts. If the license is a requirement rather than a preference, Plunk is the answer here and we aren't in the running for it.

Nitrosend does the same three jobs with a different operator in mind. Campaigns, flows, and segments are MCP tools before they're screens, contacts are unlimited on every plan, and a published ladder replaces a rate that climbs in a straight line. The team that should switch is one already running email through an agent that can trigger their automations but can't author one. The comparison index covers the hosted alternatives if the license isn't the deciding factor.

Pricing math

What you actually pay.

Both published ladders, monthly, in US dollars. Read Plunk's column as one rate applied to volume rather than as a plan ladder: there's no volume break on it, so the bottom three rows are arithmetic at $0.001 an email rather than quoted plan prices.

Scenario	Nitrosend	Plunk
Free	8,000 emails to start, then 500/mo forever. Unlimited contacts, full MCP, API, and CLI	1,000 emails/mo forever. Unlimited contacts, no credit card, Plunk branding on the emails
10,000 emails/mo	$20 Pro: 20,000 included, BYO sending and AI keys	$10 at $0.001 an email, no base fee and no minimum
100,000 emails/mo	$100 Ultra: 125,000 included, 5 brands, 10 seats	$100 at the same rate, with no volume break on the way up
1M emails/mo	$300 Enterprise: 500K to 4M+ at a published price	$1,000 at the same rate

Prices accurate as of August 2026. Check vendor sites for current rates.

Migration

How to switch (or run both).

Nothing here is big-bang. Plunk keeps sending for as long as the overlap runs, and the last step is the one that makes the whole move reversible, so none of it has to be settled on day one.

Add and verify your sending domain in Nitrosend. DKIM and SPF records sit alongside Plunk's, so both platforms can send from the same domain while you work through the rest of this list.
Move one message type first: a receipt or a password reset. Plunk's POST /v1/send and nitro_send_message take the same single-recipient shape, so this is a base URL and a payload change rather than a rewrite. Watch it for a week.
Pull your contacts with GET /contacts, custom fields and all, then load them with nitro_import_contacts. The export is an API call on both sides, so nobody waits on a support ticket for a CSV.
Rebuild each automation as a flow with nitro_compose_flow, one at a time. Plunk's builder has no documented export, so this step is a rebuild rather than a port, and it's the one that needs a person in front of it.
Keep the reputation you already have. A self-hosted Plunk sends through AWS SES keys you hold, and BYO sending keys on Pro and above take those same keys, so the transport, the warmed identity, and the SES history stay put while the platform above them changes.

Honest credit

What Plunk does well.

Picking a tool is about fit. Here's what Plunk is genuinely good at.

Open source: the whole platform is the repository under AGPL-3.0, not a trimmed edition wrapped around a hosted core.
Self-hosting: a published Docker image and a documented deployment guide, so it runs inside infrastructure you control.
One product: transactional, campaigns, workflows, segments, and analytics ship together rather than as modules bought separately.
Workflow builder: triggers, delays, and conditional logic, built visually and without writing code.
Flat pricing: $0.001 an email, with no base fee and no minimum.
No feature tiers: every capability is on the free plan as well as the paid one.
Spend cap: an optional monthly ceiling, which is rare on usage-based pricing.
Unlimited contacts: on both plans, so the bill tracks what you send rather than what you store.
API reach: campaigns, contacts, segments, and templates are all addressable with an API key, not only transactional send.
A published OpenAPI spec: it sits in the repository, so the surface is machine-readable rather than prose only.
Key hygiene: public and secret keys are separated, and event tracking accepts only the public one.
Inbound email: receiving mail with custom routing rules is a real product feature here.
SMTP relay: an existing framework can point at Plunk without a code change.

What Nitrosend adds

Where we think we're better.

MCP-first: every capability is an API endpoint and an MCP tool before it's a screen.
Flows an agent composes: the MCP covers campaigns, flows, contacts, templates, and segments.
Where the other surface stops: Plunk's published API reference documents no workflow endpoints, so its automation builder is where an agent stops.
Triggering isn't authoring: an event fires a Plunk workflow that the same code can't write, which is a different thing from running the automation.
The awkward four are tools too: deliverability, billing, tests, and approvals are the ones that usually stop an automation dead.
Reputation data in reach: bounce rates, complaint rates, and domain reputation are readable by the same agent that sends the mail.
Transactional stays on REST: a send that has to be fast shouldn't wait on a tool call, so it goes through the API rather than the agent.
BYO sending keys: Amazon SES, Resend, Postmark, Mailgun, and SendGrid on Pro and above.
A reversible move: a self-hosted Plunk already sends on SES keys you hold, and those are keys we take.
A published price at scale: 500,000 to 4M+ emails a month on Enterprise, where a flat rate keeps climbing in a straight line.
Managed: no Docker stack to run, no Postgres to hold, and no SES account to configure.

Use case fit

When to pick which.

Pick Plunk if

The license is a requirement rather than a preference, or you want to self-host and hold your own data. It's also the call when you're under roughly 100,000 emails a month and the per-email rate is the deciding number, when you already run AWS SES and want a control plane over it, or when your product receives mail as well as sending it. Nitrosend isn't open source and isn't self-hostable, so neither is a close call.

Pick Nitrosend if

You already run email through an agent and keep hitting a screen at the last step, or you want automations composed by an agent rather than only triggered by one. It points the same way when you're past the volume where a flat per-email rate stops being the cheap answer, or when you'd rather not hold a database and an SES account just to send email. The clearest case is a team whose workflows are the exact thing they'd want an agent to write. Shortlists that reach this point often also weigh Zepic, Zoho Campaigns, and Woodpecker depending on whether the mail is lifecycle, bundled, or outbound.

Both of these run on somebody else's transport

A self-hosted Plunk lists AWS SES credentials as required configuration. The region, the access key ID, and the secret all have to be filled in before the stack will send at all, which means the thing you're running is a control plane over a transport you already own.

That's the same architecture as BYO sending keys, and it's why moving between the two is unusually cheap. Nobody has to change who delivers the mail on the day they change platforms, and the email API takes the same send either way. The domain stays authenticated, the identity stays warmed, and the only layer that moves is the one composing the messages.

Where it runs out is ownership of the control plane itself. If you want that in a repository you can read, on hardware you hold, under a license nobody can revoke, that's Plunk and we don't have an answer for it.

The question is who operates it

Plunk's operator is a developer with an API key and a person in the workflow builder. Its API reaches campaigns and segments as well as transactional sends, and the builder is designed well for someone sitting in front of it. Read the product that way and it holds up.

Ours is an agent, so flows are MCP tools before they're screens. That ordering is the difference, and it isn't an endpoint count: an agent surface added on top of a builder reaches the objects a person already made, so triggering an automation is a call and authoring one stays a screen. The pattern we see is a team getting an agent as far as drafting the campaign, checking the domain, and queuing the send, then stopping at the one screen that authors the automation. That last screen is the reason the flow surface exists as MCP.

Where it runs out: if nobody on your team works through an agent yet, the difference is theoretical, and the pricing table above is the honest reason to choose. If somebody does, start on the free tier and compose one flow through the agent you already use. An afternoon is enough to find out whether that last screen was the problem.

Plunk vs Nitrosend - common questions.

Is Nitrosend open source, and can I self-host it?

No to both. Nitrosend is a hosted platform and there's no source-available or self-hosted edition of it. If the license is a requirement rather than a preference, or the data has to sit on infrastructure you control, Plunk is the answer and nothing on this page argues otherwise.

Can I keep my AWS SES sending reputation if I move off a self-hosted Plunk?

Yes, and that's the route we'd recommend. The mail is going out through your own AWS SES account, so pointing Nitrosend at the same account with BYO sending keys on Pro and above means delivery carries on from an identity that's already warm. What changes is the software composing and scheduling the mail, not the infrastructure sending it.

Can an agent run campaigns and automations on Plunk?

Campaigns yes, automations not really. Plunk's published API covers listing, creating, and sending a campaign, and it documents no workflow endpoints, so code triggers an automation by posting an event and can't author one. There's no MCP server either. Nitrosend exposes flows as MCP tools alongside campaigns and segments.

Which one is cheaper, Nitrosend or Plunk?

It depends where you sit. Plunk is cheaper below roughly 100,000 emails a month, the two are about level around there, and above it a published plan ladder wins: a million emails a month is $1,000 at a flat $0.001 an email, against $300 on our Enterprise tier.

Start with the free tier.

8,000 emails to start, then 500 a month, unlimited contacts, full MCP, API and CLI access. No credit card.