coss.com vs Resend
Resend and coss.com cover much of the same email ground. coss.com puts sub-accounts, sandbox environments and SMS on the same key.
Both are developer-first email APIs with SDKs, receiving and inboxes for agents. Resend has automations and a more collaborative inbox. coss.com is the choice when you send for your own customers, want a sandbox per environment, or need email next to SMS and one-time codes.
At a glance
Resend's side was checked on against its own pages. Prices are list prices.
| Feature | coss.com | Resend |
|---|---|---|
| Pricing model | Per recipient, with no volume tiers to pick: $0.40 per 1,000 recipients for the first 1,000,000; $0.30 per 1,000 recipients from 1,000,001 to 10,000,000; $0.22 per 1,000 recipients beyond 10,000,000. Paid plans start at $25/month, all of it spendable on usage | Monthly plans by email volume (Pro from $20/month for 50,000 emails, Scale from $90/month for 100,000); marketing priced by contacts (Pro marketing from $40/month for 5,000) |
| Free tier | Free plan: 3,000 email recipients a month, 3,000 received emails a month and 3 inboxes; 1 sending domain | 3,000 emails a month, at most 100 a day, 3 domains |
| Transactional email | REST API and an SMTP relay (smtp.coss.com), batch and scheduled sends, idempotency keys, templates with versions and locales | REST API and SMTP, templates with an editor |
| Marketing email | Contacts with custom properties, audiences, segments, topics with a hosted preference center and double opt-in, broadcasts on a separate marketing stream | Contacts, segments, topics, broadcasts and automations (10,000 automation runs a month included) |
| Receiving email | Every environment has its own address under coss.com's inbound domain, or receive at your own domain with one MX record; an email.received webhook, content and attachments through the API | Any address at a Resend-managed .resend.app subdomain, or your domain with an MX record; a webhook, then the content through its receiving API |
| Inboxes for agents | Inboxes give each agent its own address: mail kept as threads, replies from the same address; 3 inboxes included | Inboxes with threads, labels, drafts, folders, assignment and a configurable agent; 3 included, more at $1 per inbox a month |
| Multi-tenant sending | Sub-accounts on Scale and Enterprise: each with its own domains, SES tenant, reputation, quotas and suppression list (transactional email) | Its multi-tenant guide offers one account with domain-scoped API keys (one shared reputation) or a separate Resend account per tenant |
| Dedicated IPs | An add-on on Scale and Enterprise: Amazon SES managed dedicated IPs, warmed up automatically | $30/month add-on on Scale, for senders above 3,000 emails a day |
| Other channels | SMS, Verify (one-time codes), Hooks (webhooks as a service) and Risk on the same API key and SDK | |
| SDKs | TypeScript, plus generated SDKs for Python, Go, Ruby, PHP, Java and .NET; Laravel, Rails and Django mail drivers; a CLI and an MCP server | Node.js, PHP (and Laravel), Python, Ruby, Go, Java, Rust and .NET |
| Webhooks | Standard Webhooks signatures, automatic retries, test events and `coss listen` to forward events to localhost | Signed with Svix headers, with secret rotation through the API |
| Logs | Every API request, email event and webhook attempt of an environment, searchable and exportable; log drains on Scale and Enterprise | API logs in the dashboard and the API; 30 days of data retention on Free, Pro and Scale |
Which to choose
Both are good at what they do. Here is where each one fits better.
Choose Resend when
You want automations
Resend runs automation workflows on contacts. coss.com's marketing email is broadcasts you write and schedule, with segments and topics deciding who gets them.
Your team works in the inbox
Resend's inboxes have labels, drafts, folders and assignment to teammates, and an agent you configure in the dashboard. coss.com's inboxes are threads an agent reads and replies to through the API.
You write Rust or Elixir
Resend has an official Rust SDK and an Elixir quickstart. coss.com's SDKs cover TypeScript, Python, Go, Ruby, PHP, Java and .NET.
Choose coss.com when
You send for your own customers
A coss.com sub-account gives each of your users their own domains, SES tenant, reputation, quotas and suppressions, so one bad sender pauses only itself. Available on Scale and Enterprise; sandbox sub-accounts are free.
You want a real sandbox
Every project has sandbox environments whose coss_test_ keys run the same API with nothing leaving coss.com, and a mailbox simulator for bounces and complaints.
Email is one channel of several
SMS, one-time codes (Verify), Hooks and Risk use the same API key, SDK, webhooks and logs as email.
You debug from logs
Each environment's log holds every API request, email event and webhook attempt, with lines about one email read as a single timeline.
Moving from Resend
- 1
Import your Resend account
The dashboard's Import page reads your account with a full-access Resend key and brings over domains, templates, contacts with their properties, segments as audiences, topics, suppressions and webhook endpoints. Nothing changes at Resend.
Read the guide - 2
Verify your domains
Add coss.com's DNS records next to Resend's. Both can sign your mail, so you keep sending through Resend until you switch.
Read the guide - 3
Switch your code and webhooks
Replace the Resend client with coss.email.send(), which takes the same kind of fields (and React Email components), or point SMTP at smtp.coss.com. Imported webhook endpoints start disabled: update your handler to coss.com's events and signatures, then enable them.
Read the guide
Questions
- Can I move my Resend account to coss.com?
- Yes. The dashboard's Import page copies domains, templates, contacts, segments, topics, suppressions and webhook endpoints from Resend with a full-access API key, and only reads your Resend account.
- Does coss.com work with React Email?
- Yes. Pass a React Email component as react to coss.email.send() and the SDK renders it into HTML and plain text, with @react-email/render installed as an optional peer dependency.
- Does coss.com have inboxes for AI agents like Resend?
- Yes. A coss.com inbox is an address for an agent: mail to it is kept as threads, an inbox.message.received webhook announces each message, and the agent replies from the same address through the API.
- Is coss.com cheaper than Resend?
- It depends on your volume. coss.com charges per recipient with no volume tiers, and a paid plan's fee is credit spent on usage; Resend sells monthly plans by email volume and marketing plans by contacts. Compare both pricing pages with your own numbers.
- Do I have to change my webhook handler when I leave Resend?
- Yes. coss.com has its own event names and signs requests with Standard Webhooks headers, so imported endpoints are created disabled with new secrets until your handler is updated.
Sources
Resend's facts were checked on ; their pages are the final word on their prices and features.
The coss.com side
- Emailcoss.com Email is a transactional email API. Send single, batch and scheduled email from your domains, with templates, tracking and per-recipient webhooks.
- Marketing emailcoss.com Marketing email sends newsletters and announcements to your contacts as broadcasts, with audiences, segments, topics and a hosted preference center.
- Inbound emailcoss.com Inbound email receives mail at your domain or at an address coss.com gives each environment, and calls your webhook with every message, parsed.
- Inboxescoss.com Inboxes give every AI agent its own email address. Mail arrives as threads with a webhook per message, and the agent replies from the same address.
Try coss.com next to Resend.
A development key costs nothing and delivers nothing, so you can compare with real code.
Add coss.com to this project: read https://coss.com/llms.txt, get a development key with `npx coss-cli init --agents`, and build and test with it.