Thanks for signing up.
", }); ``` **Reloop** ```typescript const reloop = new Reloop({ apiKey: process.env.RELOOP_API_KEY! }); const { response, emailError } = await reloop.mail.send({ from: "AcmeThanks for signing up.
", }); ``` The details: | | Reloop | useSend | |---|---|---| | Endpoint | `POST /api/mail/v1/send` | `POST /api/v1/emails` | | Field style | `reply_to`, `scheduled_at` (snake_case) | `replyTo`, `scheduledAt` (camelCase) | | Idempotent retries | `Idempotency-Key` header | `Idempotency-Key` header | | Scheduling | Yes | Yes, plus update and cancel endpoints | | Stored templates | Yes, `{{{variables}}}` | Yes, by `templateId` with `variables` | | Error format | `message`, `why` and `fix` | Not documented | | Official SDKs | Node, Python, Go, PHP, Ruby, Rust, Java, .NET, Elixir | Node, Python, Go | useSend has two nice touches worth calling out: endpoints to **update or cancel a scheduled email**, and a visual **email editor** for campaigns, built on Tiptap and jsx-email. Reloop's strong opinion is its error shape. A failed send tells you **why** it failed and **how to fix it**: ```json { "message": "Domain not found", "why": "The domain mail.acme.com was not found or is not authorized for your organization", "fix": "Ensure the domain is registered and verified in your dashboard" } ``` ### Webhooks Both sign webhooks with HMAC-SHA256. - **useSend** sends `X-UseSend-Signature` and `X-UseSend-Timestamp`, retries up to six times with exponential backoff, and turns a webhook off after 30 failures in a row. Events cover emails, contacts and domains. [Docs](https://docs.usesend.com/guides/webhooks). - **Reloop** sends a `Reloop-Signature` header, with events like `email.delivered`, `email.bounced`, `email.complained` and `email.received`. --- ## Self-hosting: the real difference This is where the two projects split. **useSend is a layer on top of Amazon SES.** Its [self-hosting guide](https://docs.usesend.com/self-hosting/overview) asks you to: 1. Run PostgreSQL and Redis (docker-compose does it for you). 2. Create an AWS IAM user with SES and SNS access. 3. Get your SES account **out of the sandbox**, which needs an AWS review. 4. Expose a public callback URL so SNS can report delivery events back. 5. Set up GitHub OAuth for logins. That's a good trade if you already live in AWS. SES is cheap, Amazon handles IP reputation, and you skip running a mail server. **Reloop ships its own mail server** (KumoMTA). You need a server with [2 vCPUs and 4 GB of RAM](/docs/self-host/requirements) at minimum, port 25 open, and DNS. There's no AWS account, no sandbox review, and no per-email fee to anyone. Install it with [one command](/self-host) or on [Coolify](/blog/reloop-coolify-setup). The flip side: **with Reloop you own your IP reputation.** Warming new IPs and watching blocklists is your job. Our free [blocklist checker](/tools/blocklist-checker) and [domain reputation checker](/tools/domain-reputation-checker) help, and the [self-hosting guide](/blog/self-hosted-email-infrastructure) covers what that really involves. | | Reloop | useSend | |---|---|---| | Sends through | Its own MTA | Amazon SES | | AWS account needed | No | Yes | | Approval before sending | No | SES sandbox exit | | Per-email cost when self-hosted | None | SES fee | | IP reputation | Yours to manage | Managed by AWS | | One-click deploy | Installer script, Coolify | Docker, Railway | --- ## Licensing Both are open source, under different licenses. - **useSend is AGPL-3.0.** You can self-host freely, but if you modify it and offer it to others over a network, you must publish your changes. - **Reloop is Apache 2.0.** It's a permissive license: you can modify it, embed it in your product, and keep your changes private. For most teams that just run it internally, both are fine. If you plan to build a product on top, Apache 2.0 gives you more room. --- ## Receiving email and agent inboxes **useSend** lists inbound email as a roadmap item in its README, so today it's a sending platform. **Reloop** receives mail into **mailboxes**. Messages are stored, threaded, spam-scored with Rspamd, and readable over the API, the [MCP server](/docs/integrations/ai-tools/mcp-server) or IMAP. You can reply in-thread with one call. That matters if you're building: - **AI agents that handle email.** Give an agent its own address and let it read and reply. See [build an AI agent that reads and replies to email](/blog/build-ai-agent-sends-emails). - **Support or shared inboxes** where humans and agents work the same threads. - **Reply handling** for transactional mail. --- ## Marketing and automations Both handle more than transactional mail. - **useSend** has contact books, campaigns with scheduling, double opt-in, and the visual editor. It manages unsubscribes for you. - **Reloop** has contacts with custom properties, groups, subscription channels, scheduled campaigns, and **event-triggered automations**. Call `reloop.automations.start` when a user signs up and a sequence of delays, conditions and emails runs. See [welcome sequences that convert](/blog/welcome-email-sequences-that-convert). --- ## Where useSend is the better choice - **You send millions of transactional emails a month** on the hosted plan. Its $0.40 per 1,000 beats our overage. - **You're already deep in AWS** and want SES's managed reputation without running a mail server. - **You want a visual editor** for marketing emails out of the box. - **You're happy with AGPL** and like how small and focused the codebase is. ## Where Reloop is the better choice - **You send under about 250k emails a month.** Plans are cheaper. - **You want to self-host without AWS**, with no sandbox review and no per-email fee. - **You need inbound mail as real inboxes**, especially for AI agents. - **You need event-triggered automations** or a dedicated IP on a $20 plan. - **You want a permissive license** to build on. --- ## Switching from useSend to Reloop 1. **Add your domain in Reloop** and publish the DKIM record (`reloop._domainkey`). Merge `include:reloop.sh` into your SPF record; don't add a second SPF record. Remove the SES records once you've fully moved. 2. **Swap the client.** Replace `usesend.emails.send` with `reloop.mail.send`, and rename `replyTo` → `reply_to` and `scheduledAt` → `scheduled_at`. 3. **Move templates.** Recreate them in Reloop with triple-brace placeholders: `{{{first_name}}}`. 4. **Export contacts** and import them into Reloop, keeping unsubscribed contacts marked as unsubscribed. 5. **Point webhooks** at a handler that verifies `Reloop-Signature`. 6. **Ramp traffic** from 10% to 100% over a week or two. If you use SMTP instead, change the host to `smtp.reloop.sh` and use your Reloop API key as both username and password. Our [SendGrid migration guide](/blog/migrating-from-sendgrid) covers the traffic split in more detail. --- ## FAQ