Knock

What Knock is

Knock calls itself customer engagement infrastructure: one platform for product, marketing and transactional messaging across email, SMS, push, chat and in-app. It is built for teams where engineering, product, growth and marketing share the work of talking to users, and its own blog names product-led SaaS companies, marketplaces and platforms as the strongest fit. Customer quotes on the homepage come from engineers at Vercel, Webflow, Amplitude, Discogs, Clay, Causal and Nellis Auction, and the company says Knock powers notifications for Vercel, Webflow, Zapier and many other organizations.

One point matters for anyone comparing email tools. Knock is an orchestration layer, not a mail server. Its own blog says you still need a transactional email service to handle delivery and deliverability, and that Knock then sits on top of it: templates, workflows, preferences, logging and cross-channel routing. The same post says Knock can connect to the providers it reviews without service-specific integration code, and that it can fall back to a second provider if the first one fails.

Workflows, broadcasts and guides

The product menu lists Workflows, Broadcasts, Guides and Agents. Workflows are the core: event-driven flows triggered from API calls, usage events or segment changes, which can send across all five channels from a single workflow. Knock's blog lists the building blocks as delays, batching and throttling. Batching collapses several notifications about one topic into a single message, throttling protects users from notification fatigue, and the company says its delays run longer than many other providers support, which matters for multi-step email flows spread over days. There are retry and delivery logic and logs underneath.

Knock's email marketing guide stresses that this is meant to be shared work. Product managers and marketers design automations in a visual workflow editor, while developers keep control through version-controlled templates and the API. The solutions menu reflects the same split, with separate pages for engineering, growth and product, and marketing operations. Reusable email components keep layouts consistent across campaigns, and the guide says non-technical staff can change those layouts without touching code.

Broadcasts cover one-off sends to an audience, the campaign side of the product. Guides are in-app messages built with your own components: paywalls, dialogs and nudges that non-engineers can then edit for copy and targeting inside Knock.

User controls are part of the platform. A preference center lets each user choose which messages they get and on which channel, and send windows keep messages inside hours the user will accept.

Templates and the editor

Email templates are built in a drag-and-drop editor, or in markdown or raw code for those who prefer it, and they follow your own layout and design system. Templates are managed collaboratively with live previews of any message type and built-in version control, so a change can be tested without touching production and rolled back with a click. Client-specific device previews come on the enterprise plan. The homepage adds AI generation of what it calls client-safe emails in your own layout and branding, and AI-powered content, logic and targeting for personalization.

Data and segmentation

Knock ingests real-time data from your product, tools and warehouse. The homepage lists a warehouse, a CDP, reverse ETL and webhooks as sources. Segments are dynamic and built from attributes, events and relations, and custom objects can be synced to power both audiences and personalized templates. Sending and engagement data is normalized across providers, so reporting looks the same whichever email service delivers the mail.

Built for developers and agents

The developer side is where Knock puts most of its weight. SDKs are listed for Node, Python, Ruby, Java, .NET, Elixir and PHP, and a customer quote describes installing the React SDK for in-app notifications. The Knock CLI and an MCP server bring the account into AI code editors, and the homepage names Cursor, Claude and Codex. Environments, version control and CI/CD integration let a team validate changes before deploying to production, and the product menu lists infrastructure as code.

Agents are the newest part of the product. The homepage invites you to describe what you are building, build a broadcast or improve existing messaging with a prompt, and says complex journeys can be built from a single prompt.

Observability is built in: every notification can be debugged from detailed logs, delivery can be tracked in real time, and logs can be streamed to external tools. One customer quote says support staff can now see the whole history of a notification, from template to delivered message.

Plans and pricing

Knock prices by messages sent, not by contacts. Its email marketing guide lists a free Developer tier with 10,000 messages a month, and a Starter plan from $250 a month for 50,000 messages that removes Knock branding. Above 50,000 notifications a month the Enterprise plan is quoted by sales, with volume discounts and enterprise features such as multi-tenancy and granular permissions. Knock's own blog names the gap between the free tier and paid plans as a weakness for hobbyists and small projects.

Reliability, security and compliance

The homepage claims 99.99% uptime, says Knock takes being a downstream provider seriously, and states that it delivers hundreds of millions of messages per month. The same section shows HIPAA, SOC2, GDPR and CCPA badges, and the footer links to a security page and an API status page. Knock's transactional email post says the company has sent billions of emails across ten providers.

Support and resources

Resources listed on the site include documentation, a quick start, tutorials, example apps, an API reference, GitHub, a changelog, manuals, templates and tools. The blog adds that you can sign up for a free account or chat with the team, and a demo can be booked from the homepage.

Who it suits

Knock suits a SaaS company, marketplace or app with engineers on hand that wants transactional, product and lifecycle messaging managed in one place, and wants marketers and product managers to edit templates and targeting without filing tickets. It is especially useful to a team that already has an email service for delivery and needs the workflow, preference and multi-channel layer above it.

It fits less well for a solo newsletter writer or a small shop that wants an all-in-one tool with its own sending, since Knock expects a separate email provider. Its own blog concedes a learning curve for less technical teams on complex implementations.