{"id":36904,"date":"2025-07-17T13:38:16","date_gmt":"2025-07-17T13:38:16","guid":{"rendered":"https:\/\/fidelissecurity.com\/?post_type=glossary&#038;p=36904"},"modified":"2025-07-17T13:49:07","modified_gmt":"2025-07-17T13:49:07","slug":"smtp","status":"publish","type":"glossary","link":"https:\/\/fidelissecurity.com\/es\/glossary\/smtp\/","title":{"rendered":"SMTP"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"36904\" class=\"elementor elementor-36904\" data-elementor-settings=\"{&quot;ha_cmc_init_switcher&quot;:&quot;no&quot;}\" data-elementor-post-type=\"glossary\">\n\t\t\t\t<div class=\"elementor-element elementor-element-550b46da e-ecs-flex e-flex e-con-boxed e-con e-parent\" data-id=\"550b46da\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;ecs_container_type&quot;:&quot;flex&quot;,&quot;_ha_eqh_enable&quot;:false}\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-2fb6eb22 elementor-widget elementor-widget-text-editor\" data-id=\"2fb6eb22\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><span class=\"TextRun SCXW212384080 BCX0\" lang=\"EN-US\" xml:lang=\"EN-US\" data-contrast=\"auto\"><span class=\"NormalTextRun SCXW212384080 BCX0\">Simple Mail Transfer Protocol (SMTP) is the foundational protocol used to send and relay email messages across the internet. It defines how email clients and servers communicate, making it possible to deliver messages from a sender\u2019s inbox to the recipient\u2019s\u2014accurately and efficiently.<\/span><\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e70a05d elementor-widget elementor-widget-text-editor\" data-id=\"e70a05d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><span data-contrast=\"auto\"><em><strong>To put it simply:<\/strong><\/em> SMTP is what happens behind the scenes every time you click \u201cSend.\u201d Whether you&#8217;re using Gmail, Outlook, or any other client, SMTP ensures that your message travels from your device to the intended destination.<\/span><span data-ccp-props=\"{&quot;134233117&quot;:false,&quot;134233118&quot;:false,&quot;201341983&quot;:0,&quot;335559738&quot;:0,&quot;335559739&quot;:0,&quot;335559740&quot;:276}\">\u00a0<\/span><\/p><p><span data-contrast=\"auto\">SMTP operates over TCP, not UDP, which ensures reliable, ordered data delivery. It uses specific ports\u201425 for server-to-server communication, 587 for email submission with STARTTLS, and 465 for SMTP over SSL\/TLS encryption.<\/span><span data-ccp-props=\"{&quot;134233117&quot;:false,&quot;134233118&quot;:false,&quot;201341983&quot;:0,&quot;335559738&quot;:0,&quot;335559739&quot;:0,&quot;335559740&quot;:276}\">\u00a0<\/span><\/p><p><span data-contrast=\"auto\">Since SMTP was not designed with native security features, it has become a frequent target for attackers. SMTP vulnerabilities\u2014like <a href=\"https:\/\/fidelissecurity.com\/cybersecurity-101\/cyberattacks\/what-is-email-spoofing\/\">spoofing<\/a>, phishing, and open relay abuse\u2014make it essential to enforce additional layers of security when using the protocol.<\/span><\/p><p><strong>Today\u2019s secure SMTP environments often rely on:<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-8bb3530 elementor-icon-list--layout-traditional elementor-list-item-link-full_width elementor-widget elementor-widget-icon-list\" data-id=\"8bb3530\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"icon-list.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<ul class=\"elementor-icon-list-items\">\n\t\t\t\t\t\t\t<li class=\"elementor-icon-list-item\">\n\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-icon\">\n\t\t\t\t\t\t\t<i aria-hidden=\"true\" class=\"fas fa-check-square\"><\/i>\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-text\">SMTP with TLS or SSL to encrypt messages during transmission<\/span>\n\t\t\t\t\t\t\t\t\t<\/li>\n\t\t\t\t\t\t\t\t<li class=\"elementor-icon-list-item\">\n\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-icon\">\n\t\t\t\t\t\t\t<i aria-hidden=\"true\" class=\"fas fa-check-square\"><\/i>\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-text\">SPF, DKIM, and DMARC to verify sender authenticity and prevent spoofing <\/span>\n\t\t\t\t\t\t\t\t\t<\/li>\n\t\t\t\t\t\t\t\t<li class=\"elementor-icon-list-item\">\n\t\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-icon\">\n\t\t\t\t\t\t\t<i aria-hidden=\"true\" class=\"fas fa-check-square\"><\/i>\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t<span class=\"elementor-icon-list-text\">Authentication <A href=\"https:\/\/fidelissecurity.com\/cybersecurity-101\/network-security\/types-of-network-security-protocols\/\">protocols<\/a> to block unauthorized message submissions<\/span>\n\t\t\t\t\t\t\t\t\t<\/li>\n\t\t\t\t\t\t<\/ul>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-65d7d09 elementor-widget elementor-widget-text-editor\" data-id=\"65d7d09\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><span data-contrast=\"auto\">However, securing email isn\u2019t just about configuring ports or enabling encryption. You need visibility across your entire network to spot anomalies, protocol misuse, or stealthy SMTP attacks.<\/span><\/p><p><span data-contrast=\"auto\">This is where <a href=\"https:\/\/fidelissecurity.com\/solutions\/network-detection-and-response-ndr\/\">Fidelis Network<\/a><sup>\u00ae<\/sup> plays a critical role. It provides deep inspection of SMTP traffic, detects policy violations, flags suspicious behavior, and offers real-time alerts\u2014empowering security teams to respond quickly and accurately.<\/span><\/p><p><b><span data-contrast=\"auto\">So, what does SMTP stand for?<\/span><\/b><span data-ccp-props=\"{&quot;134233117&quot;:false,&quot;134233118&quot;:false,&quot;201341983&quot;:0,&quot;335559738&quot;:0,&quot;335559739&quot;:0,&quot;335559740&quot;:276}\">\u00a0<\/span><\/p><p><span data-contrast=\"auto\">It stands for Simple Mail Transfer Protocol\u2014but in today\u2019s threat landscape, it also stands for a communication channel you can\u2019t afford to overlook.<\/span><span data-ccp-props=\"{&quot;134233117&quot;:false,&quot;134233118&quot;:false,&quot;201341983&quot;:0,&quot;335559738&quot;:0,&quot;335559739&quot;:0,&quot;335559740&quot;:276}\">\u00a0<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-c239774 e-con-full e-ecs-flex e-flex e-con e-child\" data-id=\"c239774\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;ecs_container_type&quot;:&quot;flex&quot;,&quot;_ha_eqh_enable&quot;:false}\">\n\t\t\t\t<div class=\"elementor-element elementor-element-ec8fdc0 elementor-widget elementor-widget-heading\" data-id=\"ec8fdc0\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<div class=\"elementor-heading-title elementor-size-default\">Want to go deeper?<\/div>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-fc4a1fa elementor-widget elementor-widget-ha-post-list happy-addon ha-post-list\" data-id=\"fc4a1fa\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"ha-post-list.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t<div class=\"ha-post-list-wrapper\">\n\t\t\t\t<ul class=\"ha-post-list\" >\n\t\t\t\t\t\t\t\t\t\t\t<li class=\"ha-post-list-item\">\n\t\t\t\t\t\t\t<a href=\"https:\/\/fidelissecurity.com\/cybersecurity-101\/learn\/simple-mail-transfer-protocol-smtp\/\">\n\t\t\t\t\t\t\t\t<span class=\"ha-post-list-icon\"><i aria-hidden=\"true\" class=\"fas fa-long-arrow-alt-right\"><\/i><\/span>\t\t\t\t\t\t\t\t<div class=\"ha-post-list-content\">\n\t\t\t\t\t\t\t\t\t<h2 class=\"ha-post-list-title\">Read: What is Simple Mail Transfer Protocol: Uses and Best Practices - your essential guide to how SMTP works, where it&#039;s vulnerable, and how to secure it.<\/h2>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t<\/a>\n\t\t\t\t\t\t<\/li>\n\t\t\t\t\t\t\t\t\t<\/ul>\n\t\t\t<\/div>\n\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Learn what SMTP is, how it works for email delivery, and why 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