--- title: Microsoft working to fix Exchange Online mailbox... description: Microsoft is investigating an ongoing Exchange Online incident (EX1436407) that began July 19, where a recent infrastructure change caused excessive memory... canonical: https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Microsoft working to fix Exchange Online mailbox quarantine issue | daily.dev og:description: Microsoft is investigating an ongoing Exchange Online incident (EX1436407) that began July 19, where a recent infrastructure change caused excessive memory... og:url: https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689 og:image: https://api.daily.dev/og/posts/Ak7ItB689.png og:image:alt: Microsoft working to fix Exchange Online mailbox quarantine issue og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Microsoft working to fix Exchange Online mailbox quarantine issue **[BleepingComputer](https://daily.dev/sources/bleepingcomputer)** · 3 min read · 1 upvotes · 0 comments ## Summary Microsoft is investigating an ongoing Exchange Online incident (EX1436407) that began July 19, where a recent infrastructure change caused excessive memory consumption from unexpected indexing data, triggering an out-of-memory condition that incorrectly quarantined customer mailboxes. Affected users are unable to send or receive emails and cannot access calendars. Senders to affected mailboxes receive Non-delivery Reports (NDRs). Cleanup of excess indexing data was 72% complete as of Wednesday evening, with mailboxes gradually being restored. Microsoft has not disclosed affected regions or customer count, nor provided a full remediation timeline. This is a recurrence of a prior incident (EX1434354) and follows a pattern of similar Exchange Online quarantine bugs over the past year. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Why are Exchange Online mailboxes getting incorrectly quarantined right now? A recent infrastructure change caused excessive memory consumption from unexpected indexing data, leading to an out-of-memory condition that incorrectly quarantines affected mailboxes. This blocks some users from receiving emails, with senders getting a Non-delivery Report, and also affects calendar access. Microsoft tracks the incident as EX1436407, a recurrence of an earlier issue, EX1434354. _Admins troubleshooting Exchange Online outages can follow incident updates like this via daily.dev._ ### How much progress has Microsoft made cleaning up the Exchange Online indexing data causing mailbox quarantines? Cleanup of the excess indexing data reached 72% complete by Wednesday evening, up from 66% earlier that same afternoon. Mailboxes are being gradually removed from quarantine as memory levels are validated region by region, though Microsoft has not given a full remediation timeline or disclosed which regions or how many customers are affected. _Teams tracking Microsoft 365 service health can follow incident progress like this on daily.dev._ ## Similar posts on daily.dev - [Microsoft Exchange Online outage causes email delays, failures](https://daily.dev/posts/microsoft-exchange-online-outage-causes-email-delays-failures-iugzphfkb) · BleepingComputer · 0 upvotes · 0 comments - [Microsoft 365 hit by outage, preventing access to emails and files](https://daily.dev/posts/microsoft-365-hit-by-outage-preventing-access-to-emails-and-files-irywo2f8j) · TechCrunch · 0 upvotes · 0 comments - [Microsoft fixes Classic Outlook bug causing email delivery issues](https://daily.dev/posts/microsoft-fixes-classic-outlook-bug-causing-email-delivery-issues-7shcricl1) · BleepingComputer · 0 upvotes · 0 comments - [Exchange Online ditches mailbox recipient rate limit](https://daily.dev/posts/exchange-online-ditches-mailbox-recipient-rate-limit-95bescc1o) · The Register · 0 upvotes · 0 comments - [Microsoft tests fix for latest hours-long Outlook outage](https://daily.dev/posts/microsoft-tests-fix-for-latest-hours-long-outlook-outage-p9tn5amyy) · TechCrunch · 0 upvotes · 1 comments --- Tags: [#microsoft](https://daily.dev/tags/microsoft) [View this post on daily.dev](https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Microsoft working to fix Exchange Online mailbox quarantine issue","url":"https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689"},"datePublished":"2026-07-23T09:22:09.817Z","dateModified":"2026-09-14T08:21:18.649Z","description":"Microsoft is investigating an ongoing Exchange Online incident (EX1436407) that began July 19, where a recent infrastructure change caused excessive memory...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e51783d245b69283f03a6fbf79b8dfe0?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e51783d245b69283f03a6fbf79b8dfe0?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"BleepingComputer","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"BleepingComputer","logo":"https://media.daily.dev/image/upload/s--as8nJ3qy--/f_auto,q_auto/v1774959951/logos/bleepingcomputer?_a=BAMAMiWQ0","url":"https://daily.dev/sources/bleepingcomputer"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"microsoft","timeRequired":"PT3M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"BleepingComputer","item":"https://daily.dev/sources/bleepingcomputer"},{"@type":"ListItem","position":3,"name":"Microsoft working to fix Exchange Online mailbox quarantine issue"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/microsoft-working-to-fix-exchange-online-mailbox-quarantine-issue-ak7itb689#faq","mainEntity":[{"@type":"Question","name":"Why are Exchange Online mailboxes getting incorrectly quarantined right now?","acceptedAnswer":{"@type":"Answer","text":"A recent infrastructure change caused excessive memory consumption from unexpected indexing data, leading to an out-of-memory condition that incorrectly quarantines affected mailboxes. This blocks some users from receiving emails, with senders getting a Non-delivery Report, and also affects calendar access. Microsoft tracks the incident as EX1436407, a recurrence of an earlier issue, EX1434354. Admins troubleshooting Exchange Online outages can follow incident updates like this via daily.dev."}},{"@type":"Question","name":"How much progress has Microsoft made cleaning up the Exchange Online indexing data causing mailbox quarantines?","acceptedAnswer":{"@type":"Answer","text":"Cleanup of the excess indexing data reached 72% complete by Wednesday evening, up from 66% earlier that same afternoon. Mailboxes are being gradually removed from quarantine as memory levels are validated region by region, though Microsoft has not given a full remediation timeline or disclosed which regions or how many customers are affected. Teams tracking Microsoft 365 service health can follow incident progress like this on daily.dev."}}]} ```