What Is Resend? The Developer Email Platform Explained
Resend is an email platform for developers. Apps use its API to send transactional messages like receipts and password resets, along with marketing emails. It was built by the team behind React Email, and in 2026 it added Inboxes for receiving mail and its own mail server, Forge.
The quick answer: Resend is one of the best choices for sending email from software, with a clean developer experience, a free plan and 50,000 emails for $20 a month. If your email mostly needs to go out, it’s hard to beat. If your agents need to live in inboxes and hold conversations, also look at CarlyEmail, which we make. And if you use Resend already, you can connect it to Carly.
Resend at a glance
Checked against Resend’s site and pricing page on November 2, 2026.
| Resend | |
|---|---|
| What it is | An email API and platform for developers |
| Founder | Zeno Rocha |
| Funding | $18 million Series A led by Andreessen Horowitz |
| Free plan | 3,000 emails a month, 100 a day, 3 domains, 3 inboxes |
| Paid plans | Pro $20/month, Scale $90/month, Enterprise custom |
| Languages | Node.js, Python, Ruby, PHP, Go, Rust, Java, Elixir, .NET and more |
| Best for | Developers sending email from an app |
What Resend does
Resend started as a simpler way to send email from code. A few lines with its SDK will send a message, and it works over REST or SMTP. Over time, it has grown into a broader platform:
- Transactional email: the core product, for messages triggered by your app.
- Marketing email: campaigns from the same platform, priced separately.
- Automations: lifecycle email flows triggered by events in your app.
- Inboxes: create addresses programmatically, receive mail and work with conversations.
- Forge: Resend’s own mail transfer agent, running on IP blocks it owns.
- Deliverability tools: DMARC, BIMI and DNS monitoring, with dedicated IPs as an add-on.
- React Email: its open-source library for building emails with React components.
Resend’s Series A announcement in December 2024 named customers like Warner Brothers, Decathlon and Raycast. The platform has moved a long way since.
Resend pricing
| Plan | Price | Transactional emails | Domains | Overage |
|---|---|---|---|---|
| Free | $0 | 3,000/month, 100/day | 3 | Not available |
| Pro | $20/month | 50,000/month | 10 | $0.90 per 1,000 |
| Scale | $90/month | 100,000/month | 1,000 | $0.90 per 1,000 |
| Enterprise | Custom | Custom | Custom | Custom |
Automations include 10,000 free runs, then cost $0.0015 a run. Every plan includes three inboxes, and extras cost $1 each a month on paid plans. Inbox email uses your transactional quota. Free accounts have 30-day data retention. Our Resend pricing guide goes further into the numbers.
What Inboxes changes
Resend was a one-way service for most of its life. Inboxes, announced at its Resend Forward event, makes it two-way: you can create addresses in code, receive email, and let agents and teams work on conversations together. That brings it closer to agent email tools like AgentMail.
It’s still a young feature inside a platform built around sending. For an app that mostly sends and occasionally receives replies, having everything in one place is a real advantage. For a product where inboxes are the main thing, compare the details, especially how inbound mail affects your quota.
Resend and CarlyEmail
We make CarlyEmail, so here’s the honest version of how they differ. They are built around different jobs.
- Choose Resend for sending. At $20, you get 50,000 emails. For receipts, password resets and newsletters, that’s better value than CarlyEmail.
- Choose CarlyEmail for inboxes. It’s an email API built for agents. At $20, you get 25 inboxes and 10,000 emails with no daily cap, and it’s priced per inbox because each one receives, stores and threads conversations.
Some products use both: Resend for high-volume outbound mail, and CarlyEmail for the agent addresses that need to read and reply. Our Resend alternatives guide compares them with other senders in more detail.
How to connect Resend to Carly
Resend also works with Carly itself, which connects to thousands of apps. It takes two steps:
- Create an API key in your Resend account.
- Paste your API key into Carly on the integrations page.
Once connected, you can ask Carly by email or text to check whether a message was delivered, send a test email, or pull your sending numbers. That’s handy when a customer says a receipt never arrived and you’d rather not open a dashboard. Our Resend integration page covers more, and you can use the same connection from Claude or from ChatGPT. If you’d rather connect Resend directly to an AI tool, see our guide to the Resend MCP.
What to weigh with Resend
- It’s built for developers. A marketer can’t use it well without someone setting up code and DNS first.
- Reputation takes time. A shared IP pool is fine for most, but high-volume senders should budget for a dedicated IP.
- Its range is still growing. Automations, Inboxes and Forge are all recent additions. Older rivals have longer records at very high volume.
- Data retention. Check how long your plan keeps data if you need long audit trails.
How Resend compares
SendGrid and Mailgun are the established names, with longer track records and more enterprise history. Postmark is known for transactional deliverability. Resend’s advantage is its developer experience and modern tooling. Our guide to the best email APIs covers the full field.
FAQ
What is Resend used for?
Developers use Resend to send transactional and marketing email from their apps, and now to receive email through Inboxes.
Is Resend free?
Yes. The free plan includes 3,000 emails a month, up to 100 a day, plus 3 domains and 3 inboxes.
Does Resend work with Carly?
Yes. Paste your Resend API key on Carly’s integrations page, and Carly can check delivery, send test emails and pull your sending numbers.
What is the difference between Resend and CarlyEmail?
Resend is built around sending at volume, with inboxes as a newer addition. CarlyEmail is built around inboxes for agents. Resend is cheaper for one-way email.
Who owns React Email?
React Email is an open-source project from the Resend team.
Give your agent a real inbox
Your agent gets its own email address. People can email it, it answers in the same thread, and your personal inbox stays out of it. Start with 3 inboxes, no card needed.
Get startedSee the prompt
Read https://docs.carlyemail.com/llms.txt and set yourself up with an email address.
