Unable to Open an Old OST File After Outlook Profile or Mailbox Changes
Hi everyone, I am looking for suggestions on handling an old OST file where the original Outlook profile or mailbox is no longer available. The situation is that an OST file contains important mailbox data, but Outlook cannot open it normally after changes to the user account or profile. This can happen after a Microsoft 365 mailbox change, Exchange migration, user account removal, or when an OST file becomes damaged. Since OST files are linked to the Outlook profile and mailbox that created them, simply moving the file to another system does not always make the data accessible. Before attempting any recovery approach, I would like to understand the recommended steps: Is there any Microsoft-recommended method to access an orphaned OST file? What checks should be performed before trying to recover data from the OST? How do administrators usually handle old OST files when the original mailbox is no longer available? What is the best way to validate recovered mailbox data? I would appreciate feedback from anyone who has handled similar Outlook OST recovery scenarios after Microsoft 365 or Exchange changes.Can Microsoft 365 Copilot Access Archive Mailboxes?
After writing about the new 100GB mailbox quota for Microsoft 365 Business Tenants, I was asked if Microsoft 365 Copilot supports Exchange Online archive mailboxes. It does. Microsoft Search indexes items in archive mailboxes, so Copilot can find and use items from those mailboxes. Interestingly, the DLP policy to block external email for Copilot didn’t work. That’s definitely something to investigate! https://office365itpros.com/2026/10/08/archive-mailbox-copilot/I built a free, open-source M365 security assessment tool - looking for feedback
I work as an IT consultant, and a good chunk of my time is spent assessing Microsoft 365 environments for small and mid-sized businesses. Every engagement started the same way: connect to five different PowerShell modules, run dozens of commands across Entra ID, Exchange Online, Defender, SharePoint, and Teams, manually compare each setting against CIS benchmarks, then spend hours assembling everything into a report the client could actually read. The tools that automate this either cost thousands per year, require standing up Azure infrastructure just to run, or only cover one service area. I wanted something simpler: one command that connects, assesses, and produces a client-ready deliverable. So I built it. What M365 Assess does https://github.com/Daren9m/M365-Assess is a PowerShell-based security assessment tool that runs against a Microsoft 365 tenant and produces a comprehensive set of reports. Here is what you get from a single run: 57 automated security checks aligned to the CIS Microsoft 365 Foundations Benchmark v6.0.1, covering Entra ID, Exchange Online, Defender for Office 365, SharePoint Online, and Teams 12 compliance frameworks mapped simultaneously -- every finding is cross-referenced against NIST 800-53, NIST CSF 2.0, ISO 27001:2022, SOC 2, HIPAA, PCI DSS v4.0.1, CMMC 2.0, CISA SCuBA, and DISA STIG (plus CIS profiles for E3 L1/L2 and E5 L1/L2) 20+ CSV exports covering users, mailboxes, MFA status, admin roles, conditional access policies, mail flow rules, device compliance, and more A self-contained HTML report with an executive summary, severity badges, sortable tables, and a compliance overview dashboard -- no external dependencies, fully base64-encoded, just open it in any browser or email it directly The entire assessment is read-only. It never modifies tenant settings. Only Get-* cmdlets are used. A few things I'm proud of Real-time progress in the console. As the assessment runs, you see each check complete with live status indicators and timing. No staring at a blank terminal wondering if it hung. The HTML report is a single file. Logos, backgrounds, fonts -- everything is embedded. You can email the report as an attachment and it renders perfectly. It supports dark mode (auto-detects system preference), and all tables are sortable by clicking column headers. Compliance framework mapping. This was the feature that took the most work. The compliance overview shows coverage percentages across all 12 frameworks, with drill-down to individual controls. Each finding links back to its CIS control ID and maps to every applicable framework control. Pass/Fail detail tables. Each security check shows the CIS control reference, what was checked, what the expected value is, what the actual value is, and a clear Pass/Fail/Warning status. Findings include remediation descriptions to help prioritize fixes. Quick start If you want to try it out, it takes about 5 minutes to get running: # Install prerequisites (if you don't have them already) Install-Module Microsoft.Graph, ExchangeOnlineManagement -Scope CurrentUser Clone and run git clone https://github.com/Daren9m/M365-Assess.git cd M365-Assess .\Invoke-M365Assessment.ps1 The interactive wizard walks you through selecting assessment sections, entering your tenant ID, and choosing an authentication method (interactive browser login, certificate-based, or pre-existing connections). Results land in a timestamped folder with all CSVs and the HTML report. Requires PowerShell 7.x and runs on Windows (macOS and Linux are experimental -- I would love help testing those platforms). Cloud support M365 Assess works with: Commercial (global) tenants GCC, GCC High, and DoD environments If you work in government cloud, the tool handles the different endpoint URIs automatically. What is next This is actively maintained and I have a roadmap of improvements: More automated checks -- 140 CIS v6.0.1 controls are tracked in the registry, with 57 automated today. Expanding coverage is the top priority. Remediation commands -- PowerShell snippets and portal steps for each finding, so you can fix issues directly from the report. XLSX compliance matrix -- A spreadsheet export for audit teams who need to work in Excel. Standalone report regeneration -- Re-run the report from existing CSV data without re-assessing the tenant. I would love your feedback I have been building this for my own consulting work, but I think it could be useful to the broader community. If you try it, I would genuinely appreciate hearing: What checks should I prioritize next? Which security controls matter most in your environment? What compliance frameworks are most requested by your clients or auditors? How does the report land with non-technical stakeholders? Is the executive summary useful, or does it need work? macOS/Linux users -- does it run? What breaks? I have tested it on macOS, but not extensively. Bug reports, feature requests, and contributions are all welcome on GitHub. Repository: https://github.com/Daren9m/M365-Assess License: MIT (free for commercial and personal use) Runtime: PowerShell 7.x Thanks for reading. Happy to answer any questions in the comments.Using the Exchange Import-Export Graph API to Access Group Mailboxes
After saying that the Graph didn’t offer much support for group mailboxes, I was promptly countered with an article explaining how to use the Exchange Import-Export API to access folders and items in group mailboxes that wasn’t limited to just the Inbox. Well, the good news is that the approach works, as seen in a complete script written to prove the case, but whether I would ever use this API for a purpose it was never designed for is quite another matter. https://office365itpros.com/2026/10/07/group-mailbox-folder-items/How to Recover Data from a Damaged or Corrupted OST File When Outlook Cannot Open It
Hi everyone, I have seen several cases where users still have an old OST file but cannot access the mailbox data inside it. This usually happens after an Outlook profile is removed, a Microsoft 365 or Exchange account is changed, a mailbox is no longer available, or the OST file becomes damaged or corrupted. One common misunderstanding is that an OST file can be opened on another computer in the same way as a PST file. However, an OST file is linked to the Outlook profile and mailbox that created it. If that connection is no longer available, Outlook may not be able to open the file normally. Before trying to recover the OST data, it is worth checking a few things: Is the original Microsoft 365 or Exchange mailbox still available? Can the Outlook profile be recreated and synchronized again? Is the issue related to the OST file itself or only the Outlook profile? Do you need the complete mailbox data or only specific folders/items? If the mailbox is still available, rebuilding the Outlook profile and allowing Outlook to create a new OST may be the better approach. However, if the mailbox no longer exists, the Outlook profile has been deleted, or the OST file is damaged and contains the only available copy of the mailbox data, recovery becomes a different process. In these situations, it is important to first check what information is still readable from the OST file. Scanning and previewing the mailbox data before export can help identify available folders, emails, attachments, contacts, and calendar items before creating a new PST file. A practical OST recovery workflow usually involves: Keeping a copy of the original OST file before making any changes. Checking whether the original mailbox can still be synchronized. Scanning the OST file to identify available mailbox items. Reviewing important folders and messages. Exporting the required data to PST. Validating the resulting PST in Outlook. A detailed overview of the OST to PST conversion process, including scanning, previewing, selecting mailbox items, and exporting recoverable data, is available here: https://www.edbmails.com/pages/ost-to-pst-converter.html One important point to remember is that recovery results depend on the condition and readability of the OST file. A conversion tool can help extract available mailbox information, but it cannot recreate data that is no longer present or readable inside the source file.
Online Archive Not Working for One User
Hi, I am experiencing an issue with the online archive for one of my users. The online archive has been working correctly for this user for years, but it has not archived any emails for the past six months. I have checked the licensing, retention tags, and retention policy, and everything appears to be correctly configured. I have also tried running the Start-ManagedFolderAssistant cmdlet multiple times, but it has not resolved the issue. Other users in my organization have the same retention policy and their online archives are working correctly. I have also tried changing the retention policy for the affected user to one that is known to work for other users, but this did not resolve the issue. I have tried running several cmdlets to gather more information about the issue, including Get-Mailbox | FL RetentionPolicy, Export-MailboxDiagnosticLogs -Identity -ExtendedProperties, Get-RetentionPolicy | FL Name, Get-RetentionPolicyTag, Get-ComplianceTag, Get-Mailbox | fl *hold*, Get-MailboxStatistics | fl ManagedFolderAssistantLastRunTime, Get-Mailbox -Archive | fl *, and Get-MailboxFolderStatistics -Archive | fl *. However, none of these cmdlets have helped me identify the cause of the issue. The output from these cmdlets appears to be normal and does not indicate any issues with the mailbox or the archive mailbox. One thing I noticed is that the Get-MailboxStatistics | fl ManagedFolderAssistantLastRunTime cmdlet does not return any output for any of my users, even though I have run the Start-ManagedFolderAssistant cmdlet multiple times. I am at a loss as to what could be causing this issue and would appreciate any suggestions or guidance on how to troubleshoot it further. Thank you
Google Workspace sender stuck at SCL=5 to all Microsoft-hosted recipients
Sending email from a new domain via Google Workspace. All mail to Microsoft-hosted recipients (both Outlook.com consumer accounts and Microsoft 365 Exchange Online tenants) is being routed to junk. Authentication passes perfectly on every message. This appears to be a domain reputation cold-start issue and I am looking for guidance on how to resolve it without waiting 2-4 weeks. Affected recipients are all Microsoft-hosted recipients tested (Outlook.com consumer + Microsoft 365 Exchange Online tenants). Please help me!!! Confirmed via X-MS-Exchange-Organization-SCL: 5 and delivery header dest:J;OFR:SpamFilterAuthJ;RF:JunkEmail on all test emails including ones with normal subject lines and body text. Content makes zero difference to the score. What has already been done: SPF hardened from ~all to -all DMARC upgraded from p=none to p=quarantine IP confirmed not listed on Microsoft's delist portal (sender.office.com) Domain confirmed not listed on Spamhaus DBL or SURBL Domain registered with Google Postmaster Tools JMRP enrollment attempted — not available to Google Workspace senders as SNDS requires IP ownership Outlook.com Postmaster support request submitted
Office 365 issues
We have an end user that started with us approximately a year ago. Shortly after he started he began noticing that his status would go away on a fairly regular basis on MS Teams. We tried uninstall/reinstall, resetting, repairing and the problem persisted. Since he was a relatively new hire we were thinking it was something with his laptop so we replaced and the issue returned. Turned in a ticket with our Office 365 vendor who in turn opened a ticket with Microsoft. After some initial testing they sent a Teams install file that seemed to fix the issue. Since that time he has regularly had issues with Teams disconnecting, Outlook just stop receiving emails, while showing connected. Typically the only fix was a restart and on some occasions that did not work. Sometimes a reset or repair might fix this issue. Throughout this we did clear credential manager, caches, etc...This got a point yesterday where I created a new user profile for him, basically like a new laptop and it temporarily fixed the Teams and Outlook issue, however when attempting to sign into MS Edge it would just spin and had to use task manager to close the app. Tried a repair on the app as you cannot uninstall and same result it would hang up and have to forcibly closed. Just wondering if someone else has encountered something like this and possible fixes. Thanks
Tenant to Tenant Migration from Existing Hybrid Model
Our company was recently acquired, and the desire is to migrate our tenant into theirs. - we are in a Hybrid deployment (1 remaining OnPrem Exchange server** and using AzureAD Sync) - we are a relatively small shop (~51 accounts w/<400GB total in mailboxes, 200GB in OneDrive, very little in SharePoint) - we create users and mailboxes OnPrem and migrate them to O365 and manage them OnPrem **In preparation and testing for this, I have taken our OnPrem Exchange server out of the mailflow, pointed the MX records to O365, disabled the connectors, etc and mail flows perfectly fine. I also created a test user in our LocalAD and synced that account to O365 (didn't create a mailbox on the local Exchange server), assigned licensing and let it create an ExchangeOnline mailbox and that mail flows fine as well. - they are not hybrid - they are using Azure AD Sync. They create and manage users in their local AD and sync them to O365 (same as we do) - they do not have any OnPrem Exchange, so all of their users mailboxes are created in the cloud automatically as licenses are applied. The question is, what is the best approach? We've looked at some third party utilities for the migration that look good, but the concern with that method is what happens then to my local AD and AzureAD Sync; managing the existing users that were created, synced and then migrated; and my local users authenticating to it, etc? Are we going to be able to fully decommission the last Exchange server and not lose the ability to manage our folks. I need them to authenticate to our Local AD so do I then point AzureAD Sync to the domain in the new tenant? We talked about the possibility of simply creating the users manually in the other tenant, then exporting/importing their data to their new accounts (instead of migrating the account itself) to remove the need to maintain an OnPrem Exchange server if the users weren't created locally then migrated. How then does that affect them authenticating to our local AD since as I understand it, you cant sync from AzureAD back to a local AD. What about the possibility (same as what I wrote in BOLD above) of recreating all of the users in my local AD (with a different UPN), not creating mailboxes locally, syncing them to 0365, assigning licensing and letting the ExchangeOnline mailbox be created automatically (no mailbox migration like we are currently doing). Then we could import their PST to their new mailbox. Now, the users WOULD exist in our localAD and when we migrate that new batch of users to the new tenant, we could point AzureAD Sync to the new tenant and it should sync. AND since they never had a mailbox on our OnPrem Exchange server, there would be no need to maintain it. Appreciate any help on working through this!
Prevent Microsoft 365 meeting invites from automatically appearing in users’ calendars
Hi All, We are trying to prevent Microsoft 365 meeting invites from automatically appearing in users’ calendars as Tentative until the user explicitly accepts the invite. Setting for Outlook Classic, New Outlook and Windows or Outlook Web. Need Microsoft recommendation on this one.
