{"id":7466,"date":"2026-04-07T09:06:14","date_gmt":"2026-04-07T07:06:14","guid":{"rendered":"https:\/\/mybox.com\/help\/?post_type=manual_kb&#038;p=7466"},"modified":"2026-04-07T09:08:55","modified_gmt":"2026-04-07T07:08:55","slug":"troubleshooting-outlook-errors-0x8004210b-and-0x80042109","status":"publish","type":"manual_kb","link":"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/","title":{"rendered":"Troubleshooting Outlook Errors 0x8004210B and 0x80042109"},"content":{"rendered":"\n<div class=\"translation-block translation-block-merged\">\n<p class=\"wp-block-paragraph\">Errors <strong>0x8004210B<\/strong> and <strong>0x80042109<\/strong> occur when your email client (such as Microsoft Outlook, Outlook Express, or Windows Live Mail) cannot establish a connection with the outgoing SMTP server. This usually indicates that the connection is being timed out or blocked.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In most cases, these errors are resolved by correcting the outgoing server address or updating the port settings to bypass local network restrictions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/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-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/#Most_Common_Causes\" >Most Common Causes<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/#How_to_Resolve\" >How to Resolve<\/a><ul class='ez-toc-list-level-3' ><li class='ez-toc-heading-level-3'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/#1_Update_the_Outgoing_Server_SMTP\" >1. Update the Outgoing Server (SMTP)<\/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-errors-0x8004210b-and-0x80042109\/#2_Adjust_Connection_Ports\" >2. Adjust Connection Ports<\/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-errors-0x8004210b-and-0x80042109\/#3_Check_Authentication\" >3. Check Authentication<\/a><\/li><\/ul><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/#Practical_Implications\" >Practical Implications<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/mybox.com\/help\/en\/knowledgebase\/troubleshooting-outlook-errors-0x8004210b-and-0x80042109\/#Summary\" >Summary<\/a><\/li><\/ul><\/nav><\/div>\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Most_Common_Causes\"><\/span>Most Common Causes<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ol start=\"1\" class=\"wp-block-list\">\n<li><strong>Incorrect SMTP Host:<\/strong> Your client may be trying to connect to a non-existent or incorrect outgoing server.<\/li>\n\n\n\n<li><strong>Port Blocking:<\/strong> Many Internet Service Providers (ISPs) block the default port 25 to prevent spam, which stops Outlook from sending mail.<\/li>\n\n\n\n<li><strong>Security Software Interference:<\/strong> Aggressive settings in a firewall or antivirus program can sometimes &#8220;clip&#8221; the connection to the <strong>mybox<\/strong> mail servers.<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"How_to_Resolve\"><\/span>How to Resolve<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<\/div>\n\n<div id=\"mybox-1556420056\" 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 these errors, you must verify your account settings within Outlook. Ensure you are using the following official <strong>mybox<\/strong> configurations:<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"1_Update_the_Outgoing_Server_SMTP\"><\/span>1. Update the Outgoing Server (SMTP)<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The correct hostname for all <strong>mybox<\/strong> email accounts is:<\/p>\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>smtp.mybox.com<\/strong><\/p>\n<\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"2_Adjust_Connection_Ports\"><\/span>2. Adjust Connection Ports<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Depending on your security preferences, use one of the following port configurations:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>For SSL\/TLS (Recommended):<\/strong> Use port <strong>587<\/strong>.<\/li>\n\n\n\n<li><strong>For Non-SSL (Standard):<\/strong> Use port <strong>25<\/strong>.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"3_Check_Authentication\"><\/span>3. Check Authentication<span class=\"ez-toc-section-end\"><\/span><\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In the &#8220;More Settings&#8221; menu of Outlook, under the <strong>Outgoing Server<\/strong> tab, ensure that the checkbox <strong>&#8220;My outgoing server (SMTP) requires authentication&#8221;<\/strong> is enabled. It should use the same settings as your incoming mail server.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Practical_Implications\"><\/span>Practical Implications<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Port 587 is more reliable:<\/strong> If you are currently using port 25 and experiencing these errors, switching to port <strong>587<\/strong> with SSL enabled often resolves the issue instantly, as it is rarely blocked by ISPs.<\/li>\n\n\n\n<li><strong>Timeouts:<\/strong> If your settings are correct but the error persists, try increasing the &#8220;Server Timeouts&#8221; slider in the Advanced settings tab to 1 or 2 minutes. This gives the client more time to establish a handshake with the server.<\/li>\n\n\n\n<li><strong>What is normal:<\/strong> Once the correct port and host are saved, the &#8220;Test Account Settings&#8221; tool in Outlook should show a completed status for &#8220;Send test email message.&#8221;<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<h2 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Summary\"><\/span>Summary<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Errors <strong>0x8004210B<\/strong> and <strong>0x80042109<\/strong> are connection timeouts. By ensuring your SMTP host is set to <strong>smtp.mybox.com<\/strong> and switching to port <strong>587<\/strong>, you can ensure a stable and secure connection between your computer and the <strong>mybox<\/strong> infrastructure.<\/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-7466","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\/7466","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\/7466\/revisions"}],"predecessor-version":[{"id":7467,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb\/7466\/revisions\/7467"}],"wp:attachment":[{"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/media?parent=7466"}],"wp:term":[{"taxonomy":"manualknowledgebasecat","embeddable":true,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manualknowledgebasecat?post=7466"},{"taxonomy":"manual_kb_tag","embeddable":true,"href":"https:\/\/mybox.com\/help\/en\/wp-json\/wp\/v2\/manual_kb_tag?post=7466"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}