{"id":7479,"date":"2026-04-07T09:16:22","date_gmt":"2026-04-07T07:16:22","guid":{"rendered":"https:\/\/mybox.com\/help\/?post_type=manual_kb&#038;p=7479"},"modified":"2026-06-18T02:48:56","modified_gmt":"2026-06-18T00:48:56","slug":"troubleshooting-outlook-error-0x800ccc79","status":"publish","type":"manual_kb","link":"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/","title":{"rendered":"Troubleshooting Outlook Error 0x800CCC79"},"content":{"rendered":"\n<div class=\"translation-block translation-block-merged\">\n<p class=\"wp-block-paragraph\">Error <strong>0x800CCC79<\/strong> is a delivery failure notification accompanied by the message <strong>&#8220;Relay access denied.&#8221;<\/strong> This occurs when your email client (such as Microsoft Outlook or Windows Live Mail) tries to send an email through the <strong>mybox<\/strong> server without proving who you are first.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In the early days of the internet, mail servers allowed anyone to send mail through them. Today, to prevent spam, <strong>mybox<\/strong> requires &#8220;SMTP Authentication&#8221;\u2014essentially a digital ID check\u2014before it will &#8220;relay&#8221; your message to the recipient&#8217;s inbox.<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_86 ez-toc-wrap-left counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/#Common_Causes\" >Common Causes<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/#Distinction_Block\" >Distinction Block<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/#How_to_Resolve\" >How to Resolve<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/#Practical_Implications\" >Practical Implications<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-error-0x800ccc79\/#Summary\" >Summary<\/a><\/li><\/ul><\/nav><\/div>\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Common_Causes\"><\/span>Common Causes<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li><strong>Missing Authentication:<\/strong> The &#8220;My outgoing server (SMTP) requires authentication&#8221; box is unchecked in your Outlook settings.<\/li>\n\n\n\n<li><strong>Incorrect Credentials:<\/strong> Outlook is trying to log in to the outgoing server with a different username or password than the one used for your incoming mail.<\/li>\n\n\n\n<li><strong>Typo in Email Address:<\/strong> Occasionally, a malformed recipient address can trigger a relay error if the server cannot determine where to send the message.<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Distinction_Block\"><\/span>Distinction Block<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\"><strong>Login vs. Relay<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>Login<\/strong> is when you connect to <strong>imap.mybox.com<\/strong> to <em>read<\/em> your mail. <strong>Relay<\/strong> is when you ask <strong>smtp.mybox.com<\/strong> to <em>send<\/em> your mail to someone else. Error 0x800CCC79 means the server let you log in to read, but blocked you from sending because you didn&#8217;t provide your credentials a second time for the &#8220;relay&#8221; process.<\/p>\n<\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"How_to_Resolve\"><\/span>How to Resolve<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<\/div>\n\n<div id=\"mybox-2389656989\" class=\"mybox-content mybox-entity-placement\"><div class=\"early-access-banner-inpost\">\r\n  <div class=\"banner-left-inpost\">\r\n    <div class=\"icon-box-inpost\">\r\n      <img decoding=\"async\" src=\"https:\/\/mybox.com\/help\/wp-content\/uploads\/2026\/02\/square-info-icon.svg\" alt=\"Info\">\r\n    <\/div>\r\n    <div class=\"text-box-inpost\">\r\n      <span class=\"label-inpost\"><span class=\"translation-block translation-block-banner-text\">Early access<\/span><\/span>\r\n      <h4><span class=\"translation-block translation-block-banner-text\">Still need help?<\/span><\/h4>\r\n      <p><span class=\"translation-block translation-block-banner-text\">Contact our customer service team.<\/span><\/p>\r\n    <\/div>\r\n  <\/div>\r\n\r\n  <div class=\"banner-right-inpost\">\r\n    <a href=\"https:\/\/panel.mybox.com\/helpdesk2\/v\/list\/\" class=\"banner-button-inpost\"><span class=\"translation-block translation-block-banner-text\">Message us<\/span><\/a>\r\n  <\/div>\r\n<\/div><\/div>\n\n<div class=\"translation-block translation-block-merged\"><p class=\"wp-block-paragraph\">To fix error 0x800CCC79, you must enable SMTP authentication in your email account settings:<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>1. Enable Outgoing Authentication<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Open <strong>Outlook<\/strong> and go to <strong>File<\/strong> &gt; <strong>Account Settings<\/strong> &gt; <strong>Account Settings<\/strong>.<\/li>\n\n\n\n<li>Select your <strong>mybox<\/strong> email account and click <strong>Change<\/strong>.<\/li>\n\n\n\n<li>Click the <strong>More Settings<\/strong> button.<\/li>\n\n\n\n<li>Go to the <strong>Outgoing Server<\/strong> tab.<\/li>\n\n\n\n<li>Check the box: <strong>&#8220;My outgoing server (SMTP) requires authentication&#8221;<\/strong>.<\/li>\n\n\n\n<li>Ensure <strong>&#8220;Use same settings as my incoming mail server&#8221;<\/strong> is selected.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>2. Verify Port and Encryption<\/strong> While in the <strong>More Settings<\/strong> window, switch to the <strong>Advanced<\/strong> tab and ensure you are using the correct <strong>mybox<\/strong> infrastructure:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Outgoing Server (SMTP):<\/strong> <code>smtp.mybox.com<\/code><\/li>\n\n\n\n<li><strong>Port:<\/strong> <strong>587<\/strong><\/li>\n\n\n\n<li><strong>Encryption:<\/strong> <strong>STARTTLS<\/strong> or <strong>TLS<\/strong><\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Practical_Implications\"><\/span>Practical Implications<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Immediate Resolution:<\/strong> Once you check the authentication box, the &#8220;Relay access denied&#8221; error should disappear instantly. You can test this by clicking &#8220;Test Account Settings&#8221; in Outlook.<\/li>\n\n\n\n<li><strong>Security:<\/strong> Using authentication ensures that no one else can &#8220;spoof&#8221; your email address using the <strong>mybox<\/strong> servers. It protects your sender reputation and ensures your mail doesn&#8217;t end up in your recipients&#8217; spam folders.<\/li>\n\n\n\n<li><strong>Mobile Devices:<\/strong> If you use the same email on a smartphone, ensure the &#8220;Outgoing Mail Server&#8221; settings on your phone also have &#8220;Authentication&#8221; set to <strong>Password<\/strong>.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Summary\"><\/span>Summary<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Error 0x800CCC79 is a simple &#8220;ID check&#8221; failure. By ensuring that your client is configured to provide your username and password when sending mail to <strong>smtp.mybox.com<\/strong>, you fulfill the security requirements of the <strong>mybox<\/strong> infrastructure and ensure reliable mail delivery.<\/p>\n<\/div>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"template":"","format":"standard","manualknowledgebasecat":[41,44,45],"manual_kb_tag":[],"class_list":["post-7479","manual_kb","type-manual_kb","status-publish","format-standard","hentry","manualknowledgebasecat-email","manualknowledgebasecat-errors-receiving-messages","manualknowledgebasecat-errors-sending-messages"],"_links":{"self":[{"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb\/7479","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb"}],"about":[{"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/types\/manual_kb"}],"author":[{"embeddable":true,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":2,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb\/7479\/revisions"}],"predecessor-version":[{"id":7480,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb\/7479\/revisions\/7480"}],"wp:attachment":[{"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/media?parent=7479"}],"wp:term":[{"taxonomy":"manualknowledgebasecat","embeddable":true,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manualknowledgebasecat?post=7479"},{"taxonomy":"manual_kb_tag","embeddable":true,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb_tag?post=7479"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}