{"id":19519,"date":"2023-10-04T03:25:41","date_gmt":"2023-10-04T03:25:41","guid":{"rendered":"https:\/\/www.sandbox.backupassist.com\/blog\/?p=19519"},"modified":"2026-04-03T07:21:43","modified_gmt":"2026-04-03T07:21:43","slug":"mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","status":"publish","type":"post","link":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","title":{"rendered":"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)"},"content":{"rendered":"\n<figure class=\"wp-block-table is-style-regular\">\n  <table style=\"border-collapse:collapse;border:none;width:100%;background:#DDF1DB;border-radius:5px;\">\n    <tbody>\n      <tr>\n        <td style=\"width:9%;pading:30px;border-collapse:collapse;border:none;color:#282561;text-align:left;\"><img decoding=\"async\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2020\/01\/note.svg\"><\/td>\n        <td style=\"width:91%;pading:30px;border-collapse:collapse;border:none;color:#282561;text-align:left;\"><b>Note:<\/b> This blog article is an update to this article: <a href=\"https:\/\/www.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups\" target=\"_blank\" rel=\"noopener noreferrer\">https:\/\/www.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups<\/a>, which was published on August 29, 2023.<\/td>\n      <\/tr>\n    <\/tbody>\n  <\/table>\n<\/figure>\n\n\n\n<h2 class=\"has-text-align-center wp-block-heading\">The additional steps described below are no longer required because Microsoft has addressed the underlying issue<\/h2>\n\n\n\n<p>This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors after previously working successfully.<\/p>\n\n\n\n<p><strong>Important:<\/strong> To fix the issue completely, you must update the software AND perform some configuration changes to the backup user. See details further below.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"475\" height=\"369\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Warnings-and-errors-3.jpg\" alt=\"\" class=\"wp-image-19557\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Warnings-and-errors-3.jpg 475w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Warnings-and-errors-3-300x233.jpg 300w\" sizes=\"auto, (max-width: 475px) 100vw, 475px\" \/><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<p>After further analysis of the issue, we have now found the root cause and have implemented a solution that is more future proof.<\/p>\n\n\n\n<p>Microsoft has changed security policies which means that it now requires additional &#8220;impersonation rights&#8221; in order to fully access the mailbox. If these impersonation rights are not granted, it results in Microsoft giving a &#8220;Mailbox does not exist&#8221; error message.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Updated Solution<\/h3>\n\n\n\n<ol class=\"wp-block-list\"><li>Upgrade to BackupAssist 365 v1.19.1 or later, and<\/li><li>Grant impersonation rights to the backup user. Please follow the &#8220;<strong>Additional steps for Exchange Mailbox backups<\/strong>&#8221; as outlined below (this process should not take more than 5 minutes):<\/li><\/ol>\n\n\n\n<h4 class=\"wp-block-heading\">Additional steps for Exchange Mailbox backups<\/h4>\n\n\n\n<p>These steps can be followed for both new users of BackupAssist 365, and existing users.<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>Go to the Exchange Admin center &#8211; <a href=\"https:\/\/admin.exchange.microsoft.com\/\">https:\/\/admin.exchange.microsoft.com<\/a><\/li><li>Navigate to Roles &gt; Admin roles, and click Add role group.<\/li><\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"531\" height=\"353\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-2.jpg\" alt=\"\" class=\"wp-image-19552\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-2.jpg 531w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-2-300x199.jpg 300w\" sizes=\"auto, (max-width: 531px) 100vw, 531px\" \/><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<ol class=\"wp-block-list\" start=\"3\"><li>Give the group a name. We recommend \u201cBA365 Impersonation\u201d but the name won\u2019t make any difference to functionality.<\/li><\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"387\" height=\"282\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-3.jpg\" alt=\"\" class=\"wp-image-19553\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-3.jpg 387w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-3-300x219.jpg 300w\" sizes=\"auto, (max-width: 387px) 100vw, 387px\" \/><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<ol class=\"wp-block-list\" start=\"4\"><li>In the next step, select the ApplicationImpersonation permission, as shown below.<\/li><\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><a href=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-4.jpg\"><img loading=\"lazy\" decoding=\"async\" width=\"709\" height=\"272\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-4.jpg\" alt=\"\" class=\"wp-image-19554\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-4.jpg 709w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-4-300x115.jpg 300w\" sizes=\"auto, (max-width: 709px) 100vw, 709px\" \/><\/a><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<ol class=\"wp-block-list\" start=\"5\"><li>In the next step, add the same backup user login that you just created.<\/li><\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"467\" height=\"204\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-5.jpg\" alt=\"\" class=\"wp-image-19555\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-5.jpg 467w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-5-300x131.jpg 300w\" sizes=\"auto, (max-width: 467px) 100vw, 467px\" \/><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<ol class=\"wp-block-list\" start=\"6\"><li>Proceed to the end of the wizard, and your role group will now be ready.<\/li><\/ol>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"606\" height=\"244\" src=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-6.jpg\" alt=\"\" class=\"wp-image-19556\" srcset=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-6.jpg 606w, https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/10\/Step-6-300x121.jpg 300w\" sizes=\"auto, (max-width: 606px) 100vw, 606px\" \/><\/figure>\n\n\n\n<p><\/p>\n\n\n\n<p>You can view the full online help documentation for Setting up a Backup User here: <a rel=\"noreferrer noopener\" href=\"https:\/\/www.backupassist.com\/365\/documentation\/references\/setup-backup-user.htm\" target=\"_blank\">https:\/\/www.backupassist.com\/365\/documentation\/references\/setup-backup-user.htm<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Note: This blog article is an update to this article: https:\/\/www.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups, which was published on August 29, 2023. The additional steps described below are no longer required because Microsoft has addressed the underlying issue This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors after &#8230; <a title=\"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)\" class=\"read-more\" href=\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\">Read more <span class=\"screen-reader-text\">Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":19469,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[763],"tags":[],"class_list":["post-19519","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-backupassist-365"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v24.9 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)<\/title>\n<meta name=\"description\" content=\"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)\" \/>\n<meta property=\"og:description\" content=\"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\" \/>\n<meta property=\"og:site_name\" content=\"Cyber Resilience Blog\" \/>\n<meta property=\"article:published_time\" content=\"2023-10-04T03:25:41+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-04-03T07:21:43+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1230\" \/>\n\t<meta property=\"og:image:height\" content=\"693\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"Linus Chang\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Linus Chang\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"Article\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#article\",\"isPartOf\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\"},\"author\":{\"name\":\"Linus Chang\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/523a9a01769da254de228dbd4b1328d3\"},\"headline\":\"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)\",\"datePublished\":\"2023-10-04T03:25:41+00:00\",\"dateModified\":\"2026-04-03T07:21:43+00:00\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\"},\"wordCount\":323,\"commentCount\":0,\"publisher\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#organization\"},\"image\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage\"},\"thumbnailUrl\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg\",\"articleSection\":[\"BackupAssist 365\"],\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"CommentAction\",\"name\":\"Comment\",\"target\":[\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#respond\"]}]},{\"@type\":\"WebPage\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\",\"name\":\"\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)\",\"isPartOf\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage\"},\"image\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage\"},\"thumbnailUrl\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg\",\"datePublished\":\"2023-10-04T03:25:41+00:00\",\"dateModified\":\"2026-04-03T07:21:43+00:00\",\"description\":\"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.\",\"breadcrumb\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg\",\"contentUrl\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg\",\"width\":1230,\"height\":693},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/www.sandbox.backupassist.com\/blog\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#website\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/blog\/\",\"name\":\"Cyber Resilience Blog\",\"description\":\"Protect Your Cloud Data with BackupAssist\",\"publisher\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#organization\"},\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\/\/www.sandbox.backupassist.com\/blog\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"},{\"@type\":\"Organization\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#organization\",\"name\":\"Cyber Resilience Blog\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/blog\/\",\"logo\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/logo\/image\/\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2019\/09\/BA-Logo-Full-Logo.svg\",\"contentUrl\":\"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2019\/09\/BA-Logo-Full-Logo.svg\",\"caption\":\"Cyber Resilience Blog\"},\"image\":{\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/logo\/image\/\"}},{\"@type\":\"Person\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/523a9a01769da254de228dbd4b1328d3\",\"name\":\"Linus Chang\",\"image\":{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/image\/\",\"url\":\"https:\/\/secure.gravatar.com\/avatar\/58a69ed0d0b9928d91dec6132dccfb646cc4230839af779f185531c722b0d017?s=96&d=mm&r=g\",\"contentUrl\":\"https:\/\/secure.gravatar.com\/avatar\/58a69ed0d0b9928d91dec6132dccfb646cc4230839af779f185531c722b0d017?s=96&d=mm&r=g\",\"caption\":\"Linus Chang\"},\"description\":\"*Founder &amp; Creator, BackupAssist* Linus Chang has been writing software since he was eight years old. He founded BackupAssist in 2002 \u2014 making him one of the longest-standing voices in Windows backup and data protection \u2014 and has spent the decades since talking to IT administrators around the world about what actually goes wrong, and why. His interest in data loss isn't abstract. Early in his career, he was working at the Monash University help desk when a student came in with a floppy disk that wouldn't read. They tried everything. None of their drives could read it either. The disk held her entire PhD dissertation \u2014 years of work \u2014 and it was the only copy. She broke down in tears. There was nothing he could do. Five years later, he wrote the first version of BackupAssist. Linus holds a Bachelor of Science in Computer Science and has held Microsoft Certified Solution Developer and Sun Certified Java Programmer credentials. More recently, he has completed digital forensics and cyber-security courses through the Black Hat Conference. He has spoken on information security and cryptography at Infosecurity Europe, addressed politicians and policymakers at Australian Parliament House, presented to SMB IT administrators at the IT Pro Experts Conference, and served as a guest lecturer to Cyber Security master's students at the University of Melbourne. On this blog, Linus writes about backup strategy and the technical side of cyber-resilience \u2014 drawing on 24 years of product development and direct conversation with the IT professionals BackupAssist is built for. [Connect with Linus on LinkedIn](https:\/\/www.linkedin.com\/in\/linuschang\/)\",\"url\":\"https:\/\/www.sandbox.backupassist.com\/blog\/author\/linus-chang\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)","description":"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","og_locale":"en_US","og_type":"article","og_title":"\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)","og_description":"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.","og_url":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","og_site_name":"Cyber Resilience Blog","article_published_time":"2023-10-04T03:25:41+00:00","article_modified_time":"2026-04-03T07:21:43+00:00","og_image":[{"width":1230,"height":693,"url":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg","type":"image\/jpeg"}],"author":"Linus Chang","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Linus Chang","Est. reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#article","isPartOf":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update"},"author":{"name":"Linus Chang","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/523a9a01769da254de228dbd4b1328d3"},"headline":"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)","datePublished":"2023-10-04T03:25:41+00:00","dateModified":"2026-04-03T07:21:43+00:00","mainEntityOfPage":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update"},"wordCount":323,"commentCount":0,"publisher":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#organization"},"image":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage"},"thumbnailUrl":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg","articleSection":["BackupAssist 365"],"inLanguage":"en-US","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","url":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update","name":"\u201cMailbox does not exist\u201d errors for Microsoft 365 mailbox backups (October 2023 update)","isPartOf":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage"},"image":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage"},"thumbnailUrl":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg","datePublished":"2023-10-04T03:25:41+00:00","dateModified":"2026-04-03T07:21:43+00:00","description":"This article relates to the issue where BackupAssist 365 backups of M365 mailboxes result in \u201cMailbox does not exist\u201d errors.","breadcrumb":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#primaryimage","url":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg","contentUrl":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2023\/08\/Tech-Advisory.jpg","width":1230,"height":693},{"@type":"BreadcrumbList","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/mailbox-does-not-exist-errors-for-microsoft-365-mailbox-backups-october-2023-update#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.sandbox.backupassist.com\/blog"},{"@type":"ListItem","position":2,"name":"Full fix for &#8220;Mailbox does not exist&#8221; errors for Microsoft 365 mailbox backups (January 2025 update)"}]},{"@type":"WebSite","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#website","url":"https:\/\/www.sandbox.backupassist.com\/blog\/","name":"Cyber Resilience Blog","description":"Protect Your Cloud Data with BackupAssist","publisher":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#organization"},"potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.sandbox.backupassist.com\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"},{"@type":"Organization","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#organization","name":"Cyber Resilience Blog","url":"https:\/\/www.sandbox.backupassist.com\/blog\/","logo":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/logo\/image\/","url":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2019\/09\/BA-Logo-Full-Logo.svg","contentUrl":"https:\/\/www.sandbox.backupassist.com\/app\/uploads\/sites\/3\/2019\/09\/BA-Logo-Full-Logo.svg","caption":"Cyber Resilience Blog"},"image":{"@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/logo\/image\/"}},{"@type":"Person","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/523a9a01769da254de228dbd4b1328d3","name":"Linus Chang","image":{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/www.sandbox.backupassist.com\/blog\/#\/schema\/person\/image\/","url":"https:\/\/secure.gravatar.com\/avatar\/58a69ed0d0b9928d91dec6132dccfb646cc4230839af779f185531c722b0d017?s=96&d=mm&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/58a69ed0d0b9928d91dec6132dccfb646cc4230839af779f185531c722b0d017?s=96&d=mm&r=g","caption":"Linus Chang"},"description":"*Founder &amp; Creator, BackupAssist* Linus Chang has been writing software since he was eight years old. He founded BackupAssist in 2002 \u2014 making him one of the longest-standing voices in Windows backup and data protection \u2014 and has spent the decades since talking to IT administrators around the world about what actually goes wrong, and why. His interest in data loss isn't abstract. Early in his career, he was working at the Monash University help desk when a student came in with a floppy disk that wouldn't read. They tried everything. None of their drives could read it either. The disk held her entire PhD dissertation \u2014 years of work \u2014 and it was the only copy. She broke down in tears. There was nothing he could do. Five years later, he wrote the first version of BackupAssist. Linus holds a Bachelor of Science in Computer Science and has held Microsoft Certified Solution Developer and Sun Certified Java Programmer credentials. More recently, he has completed digital forensics and cyber-security courses through the Black Hat Conference. He has spoken on information security and cryptography at Infosecurity Europe, addressed politicians and policymakers at Australian Parliament House, presented to SMB IT administrators at the IT Pro Experts Conference, and served as a guest lecturer to Cyber Security master's students at the University of Melbourne. On this blog, Linus writes about backup strategy and the technical side of cyber-resilience \u2014 drawing on 24 years of product development and direct conversation with the IT professionals BackupAssist is built for. [Connect with Linus on LinkedIn](https:\/\/www.linkedin.com\/in\/linuschang\/)","url":"https:\/\/www.sandbox.backupassist.com\/blog\/author\/linus-chang"}]}},"_links":{"self":[{"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/posts\/19519","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/comments?post=19519"}],"version-history":[{"count":8,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/posts\/19519\/revisions"}],"predecessor-version":[{"id":19925,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/posts\/19519\/revisions\/19925"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/media\/19469"}],"wp:attachment":[{"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/media?parent=19519"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/categories?post=19519"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.sandbox.backupassist.com\/blog\/wp-json\/wp\/v2\/tags?post=19519"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}