{
  "port": 2525,
  "protocol": "tcp",
  "service": "SMTP submission (unofficial alternate)",
  "oneLiner": "The unofficial fallback SMTP submission port used when ISPs block 25, 465 and 587.",
  "whatItIs": "IANA registers 2525 as ms-v-worlds (\"MS V-Worlds\"), an individual's assignment that nothing uses — the \"ms-\" prefix is part of the service name, not an attribution to Microsoft. What actually listens here is mail submission: email service providers such as SendGrid, Mailgun and Mailjet offer 2525 as a mirror of their port 587 submission endpoint, with the same STARTTLS and SMTP AUTH requirements, because consumer ISPs and cloud providers frequently block the standard ports outbound. It is a convention, not a standard — the IETF's message submission spec (RFC 6409) defines 587, and no RFC blesses 2525.",
  "exposure": {
    "verdict": "careful",
    "note": "Acceptable only as a real submission service that requires STARTTLS and authentication, exactly like 587. Because nothing standardises 2525, verify the server actually enforces both rather than assuming it mirrors 587's policy — and never run an open relay here."
  },
  "checkCommand": "openssl s_client -starttls smtp -connect TARGET:2525",
  "links": [
    {
      "title": "RFC 6409 — Message Submission for Mail (defines port 587)",
      "url": "https://www.rfc-editor.org/rfc/rfc6409.html",
      "kind": "spec"
    },
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry — 2525 (ms-v-worlds)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=2525",
      "kind": "iana"
    }
  ],
  "ianaName": "ms-v-worlds"
}