For the complete site index, see llms.txt. Docs index: llms-docs.txt. Marketing corpus: llms-full.txt. Docs corpus: llms-full-docs.txt. Prefer markdown URLs where available (append .md).. Product skill: skill.md. Pricing: pricing.md. Docs MCP: /docs/mcp.

Free Tools

Free Email Sender Lookup

See which email providers are allowed to send as any domain, and who receives its mail. We read public MX, SPF and DKIM records and never send email. Free, no sign-up.

Best features

Why choose Reloop's email sender lookup?

Free, no account needed, and read straight from the domain's public DNS.

100% Free & No limits

This lookup is free. It needs no signup and has no credits or expiry.

Unrolls nested SPF

We follow branded includes like spf.acme.com down to the real provider underneath.

Flags leftover vendors

Providers still in SPF with no DKIM key are marked as likely leftovers you can remove.

No Account Needed

Use the lookup or the API without an account or an API key. We never send email.

Who is it for

Where can I use Reloop's email sender lookup?

Anyone who needs to know which services can send email as a domain.

Email admins

  • SPF cleanup
  • 10-lookup limit fixes
  • Vendor offboarding
  • DMARC rollout prep
  • Migration planning
  • Inbox vs. sender audits
  • Subdomain policy checks

Security teams

  • Shadow IT discovery
  • Spoofing exposure
  • +all misconfigurations
  • Vendor risk reviews
  • Phishing triage
  • M&A due diligence
  • Compliance audits

Sales & Growth

  • Tech stack research
  • Competitor ESP lookup
  • Lead enrichment
  • Account qualification
  • Migration prospecting
  • Partner vetting
  • Market mapping

Developers

  • Onboarding checks
  • Custom domain setup
  • Multi-tenant sending
  • Customer DNS support
  • Deliverability debugging
  • ESP detection APIs
  • Internal tooling
API integration

Integrate today in your code

One request returns the inbox provider, every authorized sender and the SPF policy for any domain. No API key or account needed.

Body

domainstringrequired
Domain or URL to inspect (e.g. stripe.com). We read its public MX, SPF and DKIM records; no email is sent.

Request

// No SDK, no API key: it is a plain POST.
const res = await fetch(
  "https://reloop.sh/api/tools/v1/who-sends",
  {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ domain: "stripe.com" }),
  },
);


const result = await res.json();
Sample Response
{
  "domain": "stripe.com",
  "resolvedAt": "2026-08-31T12:00:00.000Z",
  "responseTimeMs": 38,
  "verdict": "split_stack",
  "headline": "Google Workspace inbox. Mail is sent via Amazon SES and SendGrid.",
  "summary": "3 providers are authorized to send as stripe.com. Inbound mail routing and outbound delivery operate across separate stacks.",
  "disclaimer": "This is who DNS authorizes, not who sent mail last week. DNS is a permission list, not a volume log.",
  "inbox": {
    "provider": "Google Workspace",
    "exchanges": ["aspmx.l.google.com", "alt1.aspmx.l.google.com"]
  },
  "senders": [
    {
      "vendor": "Google Workspace",
      "role": "inbox_and_send",
      "confidence": "high",
      "leftover": false,
      "evidence": [
        { "type": "spf_include", "value": "_spf.google.com" },
        { "type": "dkim_selector", "value": "google" }
      ]
    },
    {
      "vendor": "Amazon SES",
      "role": "send",
      "confidence": "high",
      "leftover": false,
      "evidence": [
        { "type": "spf_include", "value": "amazonses.com" }
      ]
    }
  ],
  "unnamed": {
    "ip4": [],
    "ip6": [],
    "includes": []
  },
  "spf": {
    "published": true,
    "qualifier": "~all",
    "lookupCount": 2,
    "rawRecord": "v=spf1 include:_spf.google.com include:amazonses.com ~all"
  },
  "nextStep": {
    "title": "Consolidate sending infrastructure with Reloop",
    "body": "Replace multiple sending vendors with Reloop's developer-first SMTP and API platform for 100% inbox placement.",
    "href": "/dashboard/signup"
  },
  "subdomainNote": null
}
AI native

Look up email senders from your AI agent

Connect Claude, Cursor, or any MCP client to Reloop and let your agent see who sends email for a domain on its own.

MCP Server

Connect Reloop to your AI agent. Let Claude, Cursor, or Codex check a domain's sending stack before they act.

  1. 1

    Open Connectors

    In Claude, go to Settings → Connectors and click Add custom connector. On Team and Enterprise plans an owner adds it under Organization settings first.

    Add to Claude
  2. 2

    Paste the server URL

    Name it Reloop and use this URL. Leave the advanced OAuth fields empty; Reloop registers the client automatically.

    https://reloop.sh/mcp
  3. 3

    Connect

    Click Connect, sign in to Reloop and approve the workspace. Then turn Reloop on from the tools menu in any chat.

Learn more

Developer CLI

Send email from your terminal. Test deliveries and fix configuration without a dashboard.

Reloop CLI

v0.4.2 · Send email from your terminal

$ reloop emails send \

--to user@example.com \

--subject "Welcome to Reloop" \

--json

✓ queued → sent → delivered (78ms)

{ "id": "msg_01jh8q...", "to": "user@example.com", "status": "delivered" }

$ reloop emails send --to dev@company.com █

Learn more
All tools

Explore all free email & developer tools

More free utilities for checking deliverability, DNS records, and email authentication before you hit send.

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Too many senders?
Send it all through Reloop.

Replace scattered sending vendors with one SPF include and one API. Start with 3,000 free emails per month.

Get started freeTalk to founder

FAQ

Frequently asked questions.

We query the domain's public DNS records across global root resolvers. By parsing the SPF record's 'include:' mechanisms, resolving nested SPF delegations (depth 2), inspecting MX mail server exchanges, and testing known DKIM cryptographic selectors, we map the infrastructure back to known email service providers.

No. DNS records represent a permission authorization list, not a real-time sending log. An authorized provider may be actively sending millions of emails per day, or it may be an abandoned trial account from three years ago that was never removed from DNS.

The MX (Mail Exchange) record defines who receives email (e.g. employee inboxes on Google Workspace or Microsoft 365). Outbound senders (defined in SPF and DKIM) are the third-party platforms authorized to dispatch automated transactional or marketing emails on behalf of that domain (e.g. Amazon SES, SendGrid, Reloop, Mailchimp).

If a provider (such as Mailchimp or SendGrid) is listed in your SPF record but has no matching active DKIM signature published while other providers on your domain do sign with DKIM, it frequently indicates an old vendor that was replaced and forgotten.

RFC 7208 limits SPF evaluations to a maximum of 10 DNS lookups. Having multiple ESP includes (e.g. Google + SES + SendGrid + HubSpot + Zendesk) often exceeds 10 lookups, resulting in an SPF PermError that causes mailbox providers like Gmail and Yahoo to treat all your legitimate mail as unauthenticated.

Companies frequently use branded include domains (like 'include:spf.acme.com' or 'include:mail.acme.com') to hide or organize their records. Our analyzer queries those intermediate records to discover the actual underlying service (e.g. 'spf.acme.com → sendgrid.net').

Some organizations list raw IP addresses (e.g. 'ip4:203.0.113.0/24') in their SPF record instead of named provider hostnames. This indicates dedicated self-hosted mail servers, custom on-premise appliances, or IP flattening services.

Reloop allows you to replace multiple disparate transactional, broadcast, and notification ESP includes with a single high-performance sending record ('include:reloop.sh') while preserving your team's Google Workspace or Microsoft 365 inboxes.

Reloop