Transmit

Transmit, found at xmit.sh, is an email infrastructure platform for developers and SaaS teams. It sends three kinds of mail through one API: transactional messages such as password resets and receipts, marketing campaigns and drip sequences, and inbound mail that it receives and parses for you. The footer calls it "High-performance email infrastructure for modern teams," and the home page leads with deliverability: reputation isolation, automatic domain warmup and address validation are built into every plan rather than sold as extras. Customers can let Transmit run the sending infrastructure, or connect their own AWS account and use Transmit as the layer on top of it.

What a sender gets

One API for three kinds of email

The home page splits the product into three parts under the heading "Every email. One API." Transactional covers "Password resets, receipts, notifications," with a sub-200ms API and bounces handled automatically. Marketing covers campaigns, newsletters and drip sequences, with user segmentation, scheduled sends, and open and click tracking. Inbound receives replies and support emails, parses the content, and either routes it to a webhook or stores it in an inbox inside Transmit. A team that would otherwise run one service for app mail, another for newsletters and custom code for incoming mail can keep all three in one place.

Sending is a plain REST call. The code sample on the home page posts JSON with from, to, subject and html fields to the send endpoint at api.xmit.sh, authorized with a bearer key, and the sample tabs cover cURL, Node.js, Python, Go and SMTP, so an application that only speaks SMTP has a route in as well. The integrations section of the site carries guides for Next.js, Node.js and Python. A guide on Transmit's site adds that the sub-200ms latency for transactional sends makes the API usable from edge-deployed applications on Vercel or Cloudflare Workers without routing through an origin server. The same guide lists Transmit's log retention as 7 days and confirms inbound email support.

Templates take variables: the example prompt the site gives for its agent tooling asks for a welcome template with firstName and companyName variables, followed by a test send. The home page also says templates, logs, analytics and warmup are built in.

Deliverability tooling on every plan

Three features sit under the heading "We obsess over inbox placement," and the page says they are "Included on every plan. No add-ons. No surprises."

Domain warmup ramps a new domain's sending volume over weeks, with auto-increasing daily limits, health score monitoring and ISP-specific pacing. The guide on the site adds that Transmit watches bounce and complaint rates in real time, pauses sending automatically when either passes a configured threshold, resumes once the rates return to normal, and raises the daily limits as the domain's reputation builds, so nobody has to keep a manual warmup schedule.

Email validation blocks invalid, disposable and risky addresses before they are sent to, using syntax and MX checks, disposable-address detection and risk scoring.

Reputation isolation is the idea the platform is built around. The page says "Your sending reputation is yours alone. Isolated infrastructure means other senders can't drag you down," and lists isolated sending pools, per-domain reputation and no shared IP risk. For a multi-tenant SaaS product that sends on behalf of its own customers, the site's guide explains, each customer's sending is kept apart, so one customer's bounces or complaints do not affect another's deliverability, and nobody has to provision dedicated IPs on demand.

The home page backs this with four headline figures: 99.2% inbox placement, a spam rate under 0.1%, API latency under 200ms, and "100% Your reputation." These are the company's own figures, presented without a method.

Composer, the AI email designer

Composer builds emails from a text description. The page's pitch is "Stop fighting with drag-and-drop editors. Describe your email in plain text, iterate in seconds, and export production-ready HTML." You pick the model (GPT-4o, Claude or Gemini), define a brand kit with colors, tone and logo once and apply it everywhere, and can bring your own AI API keys to control what generation costs. The sample prompt on the page asks for a welcome email for new users in a friendly tone, with a call to action to complete their profile, in the brand's colors. For a developer team that wants finished HTML without hand-coding email markup or learning a visual builder, this is a short route from an idea to a sendable template.

MCP server and agent skill

A banner across the site announces that the MCP server is live. It runs at mcp.xmit.sh, needs no installation (paste the URL, log in, done), and exposes 18 tools and 2 workflows for managing campaigns, templates and contacts from Claude, Cursor, Windsurf, ChatGPT, Open Claw and other MCP-compatible clients. A separate Agent Skill teaches a coding agent the Transmit API with one command, npx skills add sendwithxmit/skills. Together they let a developer draft a template, add contacts or schedule a send from the assistant they already work in.

Contacts from your auth provider

For SaaS teams, Transmit pulls users straight from the authentication provider instead of relying on CSV exports. You paste the provider's API key, which Transmit encrypts with AES-256-GCM; every 6 hours new signups become contacts, with no code changes; and from there the users are ready for transactional mail, campaigns and automations. Clerk and Auth0 are available now, while Supabase, Firebase, Cognito and Okta are marked coming soon.

Plans and pricing

Transmit runs in two modes, and the home page says you can "Start managed, switch to BYOK anytime. Same API. Same dashboard. Zero downtime." The FAQ on the site describes the model as volume-based pricing, in which you pay for sends, not contacts, and the closing banner adds "Cancel anytime."

Managed by Transmit is the recommended option. Transmit runs the infrastructure, no cloud account is needed, pricing is volume-based, deliverability is handled for you, reputation is isolated per account, and domain warmup is included. It is listed at "$2 /mo to start," and the page says setup takes 2 minutes. The home page shows that starting price only, not the volume steps above it.

Bring Your Own Cloud connects your AWS account through an IAM role or access keys. You pay AWS directly, which the page puts at "~$0.10/1K," get unlimited sending volume, and keep all Transmit features, for a platform fee listed as "$0-$149 /mo + AWS costs." The guide on the site explains that in this mode you supply AWS SES credentials and Transmit works as the control plane on top, still handling warmup scheduling, bounce tracking and validation, while the sending infrastructure stays yours. It notes that the SES rate varies by region and volume tier, so the effective per-email cost depends on your own AWS account configuration.

Documentation, a changelog and an open source section sit alongside free sender tools on the site: a DNS checker, SPF and DKIM record generators and an MX lookup, plus a glossary covering SPF, DKIM and DMARC.

Who it suits

Transmit fits developers and SaaS teams who send from code and want deliverability handled rather than managed by hand. Warmup, validation and isolation come switched on, and the automatic pause on high bounce or complaint rates protects a new domain while it builds a reputation. Multi-tenant SaaS products sending on behalf of their customers are the audience the per-customer isolation is built for. Teams with an existing AWS account, or with volumes where SES pricing matters, can start managed and move to BYOK later without changing application code. Teams on Clerk or Auth0 get their user base into Transmit without writing a sync job, and teams already working in Claude, Cursor or ChatGPT can run campaigns and templates from there through the MCP server.

It is a less natural fit for a marketing department that wants a drag-and-drop editor: the product is API-first, and its designer works from text prompts. Log retention of 7 days is short if you need to trace a delivery complaint weeks after the send, and teams on Supabase, Firebase, Cognito or Okta will either wait for their sync connector or call the API themselves in the meantime.