mail@mydomain is causing a cert mismatch error in all browsers for Outlook.com
Hello, I have created a CNAME for our users in my domain so that they can access webmail. For example, it's called mail.mycustomdomain.com, and it is directed to Outlook.com But when I try to visit mail.mycustomdomain.com, it shows a security warning and recommends going back. I can understand because the SAN name in the certificate presented by Outlook doesn't include my CNAME. Is there anything I can do as a workaround so our users can enter the CNAME without encountering a Certificate Mismatch Error? It is causing repeated calls to the helpdesk, and we would like them to use something simple they can remember. Thanks
Outlook Desktop users continually prompted for credentials On-Prem Exchange SE
Battling ongoing issues with users being continually prompted for password using Outlook 2024 LTSC with on-prem Exchange 2019 SE. Removed Windows credentials, turned off cache mode, removed shared calendar(s), outlook connection status seems fine. Only (temp) workaround seems to be removing mail profile and recreating it. All other network resources on domain are fine. Any input appreciated. Thanks
Exchange SE HU6: PDF attachments truncated to 13 KB via Outlook Desktop — OWA unaffected
We've spent days isolating this and ruled out everything we could touch. The corruption survives agent disabling, Bitdefender removal, and BypassFiltering — and the message tracking logs show exactly where it happens. Environment: Exchange Server SE, Build 15.2.2562.41 (HU6 / KB5081755), Windows Server 2025 Problem: PDF attachments sent internally via Outlook Desktop (MAPI) arrive corrupted at ~13 KB (original: ~32 KB, no xref/EOF). All PDF sizes, all internal recipients affected. Started 21 May 2026. Key finding — OWA works, Outlook Desktop doesn't: Sending the identical email via OWA → attachment arrives intact. Outlook Desktop → truncated. Message tracking proof: Both paths deliver the message at full size (~42 KB) via STOREDRIVER DELIVER. Only the Outlook Desktop delivery shows an additional X-SDDS=0.106 step in the STOREDRIVER latency breakdown. That step does not appear in the OWA delivery. The corruption happens inside that MAPI/TNEF store write step — not in transport. Systematically ruled out: All transport agents disabled → still 13 KB Exchange Malware Agent + Set-MalwareFilteringServer -BypassFiltering $true → still 13 KB Bitdefender GravityZone fully uninstalled from server → still 13 KB EEMS mitigations: only PING1 and M2.1.0 applied, neither affects MAPI delivery Temporal correlation: Three Windows updates installed 21.05.2026: KB5087051 (.NET Framework 4.8.1), KB5087539 (Windows Server 2025 CU), KB5089717 (Servicing Stack). Exchange SE HU6 (KB5081755) was installed around the same period. Workaround: Sending via OWA works. Not acceptable long-term. Has anyone seen this? Is this a known regression in HU6 or KB5087051?
Feature Request: Add "Recent Activity Feed" combining Sent & Received emails
Respected Outlook Product Team, I am writing to submit a feature request aimed at improving productivity and message tracking for power users who heavily rely on Microsoft Outlook for their daily communication workflows. The Problem: Currently, Outlook separates communication into distinct folders: "Inbox" for incoming mail and "Sent Items" for outgoing mail. When managing large-scale communications—specifically when sending bulk or recurring emails via BCC (Blind Carbon Copy)—it becomes incredibly tedious to constantly switch back and forth between the Inbox and Sent Items folders to track recent operations or verify the exact sequence of historical activities. The existing "Group messages by conversation" feature also fails to merge these independent outgoing streams seamlessly unless a direct reply is received. The Solution / Feature Proposal: I highly request the product team to introduce a "Recent Activity Feed" filter or view within the main Outlook Inbox interface. Inspired by modern social media and collaboration timeline feeds, this feature should display both Sent and Received emails chronologically in a single unified message list. Incoming and outgoing messages should be clearly distinguishable using intuitive icons (e.g., incoming/outgoing arrows) and labels (e.g., "SENT (BCC)" vs "RECEIVED"). This will allow professionals to review all recent actions, sent bulk updates, and incoming threads at a single glance without breaking their operational focus. I have attached a UI/UX Concept Design image with this email to visually demonstrate how this feature would streamline the user experience seamlessly. I sincerely hope the engineering and product management teams will consider this feature in future Microsoft Outlook updates to adapt the platform to modern, high-volume workflow requirements. Thank you for your time and continuous efforts to improve Microsoft Outlook. Regards, Pawan Kumar
Microsoft 365 Outlook Classic Latest Update Copilot issues
Hello to all, we are currently using the Microsoft 365 Outlook Classic, using version Version 2604 Build 16.0.19929.20172 (Current Channel) Copilot works as expected; However ever since the next update was released (Version 2605 (Build 20026.20076)) some users including me, have been getting the below error: I have tried uninstalling and installing the latest version directly, with the same issue. Scanned for any corrupted system files with no issues,but still get the error; I have tried the update Licence from the Outlook application, with no issues but the copilot something went wrong error keeps on persisting. Internet searches are very vague and the I have found some registry suggestions which I have also tried with no solution. The only way to get Copilot working on Outlook Classic was to revert to a previous working version, only then Copilot works as expected. This only happens in Outlook Classic; Copilot works fine on the latest version of Microsoft Office 365 with Word, Excel, etc. For those that maybe might ask why not switch to the New Outlook, we have had issues with it and it has been recommended to use the Classic Outlook for the time being. Has anyone been experiencing such issues please? Thanks for any help.Outlook Cached Mode Repeatedly Re-syncs Mailbox After Restart (Starts Again Around 3.99 GB)
Hi everyone, I’m experiencing a strange Outlook Cached Exchange Mode issue with a Microsoft 365 mailbox after a recent Windows rebuild and wanted to see if anyone has seen similar behavior. Environment: Microsoft 365 mailbox (Exchange Online) Outlook for Microsoft 365 Version 2605 Build 16.0.20026.20076 64-bit Windows 11 25H2 Fresh OS rebuild performed twice New Outlook profile created Office completely reinstalled OST recreated multiple times Issue: When Cached Exchange Mode is enabled, Outlook starts downloading/synchronizing mail normally, and the OST file continues to grow correctly. However, after every reboot or Outlook restart, Outlook again shows “Downloading…” starting from around 3.99 GB. Important observations: Online Mode works perfectly OUTLOOK.EXE closes properly after exit OST file is NOT deleted and continues growing Sync slider changes (1 month, 1 year, all mail) make no difference Disabling Outlook indexing did not help New Outlook profile did not help Reinstalling Office did not help Problem only started after OS rebuild Before rebuild, same mailbox worked normally in Cached Mode No pending office or windows update. It does not appear to actually re-download the mailbox from scratch because the OST size keeps increasing, but Outlook repeatedly processes/downloads from around the same 3.99 GB point after restart. Has anyone seen: Cached Mode replaying synchronization repeatedly after restart? Similar behavior on recent Current Channel builds? Security/EDR products interfering with OST synchronization state? Any known regressions with Outlook Version 2605 Build 16.0.20026.20076? Any suggestions or similar experiences would be appreciated.
Is Office 365 E3 Developer free
Hi, My tenant had a license named "Office 365 E3 Developer" which allowed us to use Outlook / Exchange (among other Microsoft Office products). This license isn't from the Microsoft 365 Developer Program, which come with free licenses. This license costed CA$11.60 a month per user when we initially purchased it. On May 2, 2026 it still costs $11.60, but when I received my monthly invoice for this tenant, this license was free. I searched around to see whether this license became free recently, but I couldn't find any info on this. The links I found all say it's a paid license. I was wondering if there's any info on this to see why it became free? Or is it a mistake and Microsoft'll be charging us the next billing cycle? Jason
