What is Simple Mail Transfer Protocol?

Simple Mail Transfer Protocol (SMTP) is an Internet standard for transferring email messages between servers and from clients to servers, defined by the Internet Engineering Task Force (IETF) in the SMTP family of Request for Comments specifications. Expanded Explanation 1. Technical Function and Core Characteristics SMTP operates as an application-layer protocol that handles the submission and relay of email over Transmission Control Protocol (TCP), typically on ports 25, 465, and 587. It

How widely is Simple Mail Transfer Protocol used?

72 organizations in our directory are tagged Simple Mail Transfer Protocol, referenced across 9 articles and 11 open source projects.

What is Simple Mail Transfer Protocol most closely associated with?

Simple Mail Transfer Protocol is most closely associated with Server and Vulnerabilities.

Simple Mail Transfer Protocol (SMTP)

Last updated August 24, 2026

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        "author": {
          "@type": "Person",
          "name": "Vijay Sarvepalli and Renae Metcalf"
        },
        "sourceOrganization": {
          "@id": "https://decisioninsights.ai/registry/department-of-homeland-security/#organization",
          "@type": "Organization",
          "mainEntityOfPage": "https://decisioninsights.ai/registry/department-of-homeland-security/",
          "name": "Department of Homeland Security"
        },
        "url": "https://kb.cert.org/vuls/id/517845"
      },
      "url": "https://decisioninsights.ai/cisa-issues-alert-on-email-header-syntax-enabling-sender-spoofing-bypassing-authentication-protocols/"
    },
    {
      "@id": "https://decisioninsights.ai/vu517845-email-spoofing-exploits-bypass-authentication-protocols/#blogposting",
      "@type": "BlogPosting",
      "headline": "VU#517845: Email spoofing exploits bypass authentication protocols",
      "isBasedOn": {
        "@type": "CreativeWork",
        "author": {
          "@type": "Person",
          "name": "Vijay Sarvepalli and Renae Metcalf"
        },
        "sourceOrganization": {
          "@id": "https://decisioninsights.ai/registry/department-of-homeland-security/#organization",
          "@type": "Organization",
          "mainEntityOfPage": "https://decisioninsights.ai/registry/department-of-homeland-security/",
          "name": "Department of Homeland Security"
        },
        "url": "https://kb.cert.org/vuls/id/517845"
      },
      "url": "https://decisioninsights.ai/vu517845-email-spoofing-exploits-bypass-authentication-protocols/"
    },
    {
      "@id": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-may-spoof-identities-through-header-exploitation/#blogposting",
      "@type": "BlogPosting",
      "headline": "VU#517845: Authenticated SMTP users may spoof identities through header exploitation.",
      "isBasedOn": {
        "@type": "CreativeWork",
        "author": {
          "@type": "Person",
          "name": "Vijay Sarvepalli and Renae Metcalf"
        },
        "sourceOrganization": {
          "@id": "https://decisioninsights.ai/registry/department-of-homeland-security/#organization",
          "@type": "Organization",
          "mainEntityOfPage": "https://decisioninsights.ai/registry/department-of-homeland-security/",
          "name": "Department of Homeland Security"
        },
        "url": "https://kb.cert.org/vuls/id/517845"
      },
      "url": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-may-spoof-identities-through-header-exploitation/"
    },
    {
      "@id": "https://decisioninsights.ai/cisa-weekly-intelligence-brief-on-security-alerts-and-vulnerabilities-week-of-november-10-2025/#blogposting",
      "@type": "BlogPosting",
      "headline": "CISA Weekly Intelligence Brief on Security Alerts and Vulnerabilities - Week of November 10, 2025",
      "url": "https://decisioninsights.ai/cisa-weekly-intelligence-brief-on-security-alerts-and-vulnerabilities-week-of-november-10-2025/"
    },
    {
      "@id": "https://decisioninsights.ai/daily-intelligence-brief-nokia-lmt-5g-defense-solution-and-cisa-advisory-updates-november-7-2025/#blogposting",
      "@type": "BlogPosting",
      "headline": "Daily Intelligence Brief: Nokia, LMT 5G Defense Solution and CISA Advisory Updates - November 7, 2025",
      "url": "https://decisioninsights.ai/daily-intelligence-brief-nokia-lmt-5g-defense-solution-and-cisa-advisory-updates-november-7-2025/"
    },
    {
      "@id": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-can-spoof-identities-via-ambiguous-from-header/#blogposting",
      "@type": "BlogPosting",
      "headline": "VU#517845: Authenticated SMTP users can spoof identities via ambiguous From header",
      "isBasedOn": {
        "@type": "CreativeWork",
        "author": {
          "@type": "Person",
          "name": "Vijay Sarvepalli and Renae Metcalf"
        },
        "sourceOrganization": {
          "@id": "https://decisioninsights.ai/registry/department-of-homeland-security/#organization",
          "@type": "Organization",
          "mainEntityOfPage": "https://decisioninsights.ai/registry/department-of-homeland-security/",
          "name": "Department of Homeland Security"
        },
        "url": "https://kb.cert.org/vuls/id/517845"
      },
      "url": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-can-spoof-identities-via-ambiguous-from-header/"
    },
    {
      "@id": "https://decisioninsights.ai/weekly-intelligence-brief-on-security-alerts-and-vulnerabilities-week-of-november-3-2025/#blogposting",
      "@type": "BlogPosting",
      "headline": "Weekly Intelligence Brief on Security Alerts and Vulnerabilities - Week of November 3, 2025",
      "url": "https://decisioninsights.ai/weekly-intelligence-brief-on-security-alerts-and-vulnerabilities-week-of-november-3-2025/"
    },
    {
      "@id": "https://decisioninsights.ai/daily-intelligence-brief-sealsq-cambium-asus-and-more-october-29-2025/#blogposting",
      "@type": "BlogPosting",
      "headline": "Daily Intelligence Brief: SEALSQ, Cambium, ASUS, and more - October 29, 2025",
      "url": "https://decisioninsights.ai/daily-intelligence-brief-sealsq-cambium-asus-and-more-october-29-2025/"
    },
    {
      "@id": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-may-spoof-other-identities-due-to-ambiguous-from-header-interpretation/#blogposting",
      "@type": "BlogPosting",
      "headline": "VU#517845: Authenticated SMTP users may spoof other identities due to ambiguous 'From' header interpretation.",
      "isBasedOn": {
        "@type": "CreativeWork",
        "sourceOrganization": {
          "@id": "https://decisioninsights.ai/registry/department-of-homeland-security/#organization",
          "@type": "Organization",
          "mainEntityOfPage": "https://decisioninsights.ai/registry/department-of-homeland-security/",
          "name": "Department of Homeland Security"
        },
        "url": "https://kb.cert.org/vuls/id/517845"
      },
      "url": "https://decisioninsights.ai/vu517845-authenticated-smtp-users-may-spoof-other-identities-due-to-ambiguous-from-header-interpretation/"
    }
  ],
  "termCode": "SMTP",
  "url": "https://decisioninsights.ai/term/simple-mail-transfer-protocol/"
}

CollectionPage

{
  "@context": "https://schema.org",
  "@id": "https://decisioninsights.ai/term/simple-mail-transfer-protocol/",
  "@type": "CollectionPage",
  "dateModified": "2026-08-24T03:29:45Z",
  "description": "Simple Mail Transfer Protocol is an Internet-standard application-layer protocol for transmitting email between servers and from clients to servers, used in enterprise infrastructures for interoperable email delivery, integration with security controls, and alignment with authentication and policy enforcement mechanisms.",
  "isPartOf": {
    "@id": "https://decisioninsights.ai/#website"
  },
  "mainEntity": {
    "@id": "https://decisioninsights.ai/term/simple-mail-transfer-protocol/#definedterm"
  },
  "name": "Simple Mail Transfer Protocol",
  "sdDatePublished": "2026-08-24",
  "sdPublisher": {
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  "url": "https://decisioninsights.ai/term/simple-mail-transfer-protocol/"
}

What we add

Graph

A glossary entry defines a term and stops there. It doesn't show where the term is actually being used or written about. We track and link every article that covers it.

BlogPosting CISA issues alert on email header syntax enabling sender spoofing bypassing authentication protocols BlogPosting VU#517845: Email spoofing exploits bypass authentication protocols BlogPosting VU#517845: Authenticated SMTP users may spoof identities through header exploitation. and 6 more on this page

Counted facts

A dictionary definition doesn't say how often a term is actually used. This counts it across the graph -- articles that mention it, open source projects tagged with it, and the organizations tagged with it, listed here alongside the count. A term has no peer companies, and nothing here claims otherwise.

Articles mentioning this entity 9 Open source projects 11 Organizations tagged 72 Organizations acens, Adam Internet, AnubisNetworks, Barracuda Networks, Benchmark Email, BitMail, Brasil Online, Cofense, curl, Đăng Ký Tên Miền - Mua VPS, Hosting Giá Rẻ, EdgeWave, ESET, Ethernet Servers, freenet.de, GFI Software, GJ2 Internet, GMX, GoDaddy, Green Mountain Access, Hey EC Related terms Related terms (co-occurring topics)

The person who sent this agent gets an answer they can act on

Somebody dispatched this agent to evaluate Simple Mail Transfer Protocol for a real decision: a shortlist, a vendor comparison, a purchase. "Simple Mail Transfer Protocol makes X" isn't something they can act on; they need to know the claim is real and where it came from. Follow one enriched link from Act 2 and see what the agent can actually hand back to them:

The record DefinedTerm Simple Mail Transfer Protocol
One of its 9 linked records BlogPosting CISA issues alert on email header syntax enabling sender spoofing bypassing authentication protocols https://decisioninsights.ai/cisa-issues-alert-on-email-header-syntax-enabling-sender-spoofing-bypassing-authentication-protocols/
The primary source CreativeWork kb.cert.org https://kb.cert.org/vuls/id/517845 Original author: Vijay Sarvepalli and Renae Metcalf

Our summary is written by Decision Insights Threat Desk. The source keeps its own byline, credited above. Both are in the JSON.