Outlook Classic (MS 365, Exchange) calendar attachments not visible to other users

Question

Outlook Classic (MS 365, Exchange) calendar attachments not visible to other users

M Eddy 0

Our small company (5 users) has a shared calendar in Microsoft 365 that worked fine until about a week or two ago. Two of us regularly create events and add attachments, and we are both using Outlook Classic (desktop) connected to Microsoft Exchange.

I can see events and event text he creates, but I cannot see attachments he adds (which I could previously). Likewise, he can see my events and text but none of the attachments I add. If attachments are added via Outlook.com, both of us can see them online and later in Outlook Classic (desktop).

Things I’ve tried include toggling cache mode, toggling “Shared Calendar Improvements,” and checking mailbox storage limits (only ~6 of 50 GB used).

M Eddy 0 Reputation points

2026-02-11T19:39:58.17+00:00

I do not have a perfect fix for this, but after exhaustive testing (signing in/out of Outlook Desktop, disabling/enabling cached mode, rebuilding NST and OST files, turning on/off Shared Calendar improvements, creating new Group calendars, confirmed storage limit not exceeded), I believe I've narrowed it down to an issue with Microsoft 365 Version 2601. When I disabled automatic updates and reverted to Version 2511 by following these instructions (https://www.accessforever.org/post/roll-back-to-previous-versions-of-office), everything went back to normal.Long story short, there's an issue with Version 2601.

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M Eddy 0 Reputation points

2026-02-11T19:39:58.17+00:00

I do not have a perfect fix for this, but after exhaustive testing (signing in/out of Outlook Desktop, disabling/enabling cached mode, rebuilding NST and OST files, turning on/off Shared Calendar improvements, creating new Group calendars, confirmed storage limit not exceeded), I believe I've narrowed it down to an issue with Microsoft 365 Version 2601. When I disabled automatic updates and reverted to Version 2511 by following these instructions (https://www.accessforever.org/post/roll-back-to-previous-versions-of-office), everything went back to normal.Long story short, there's an issue with Version 2601.

Answer 1

Updated 2/12/2026:
Hi @M Eddy

Thank you for contacting the Microsoft Q&A forum.
I am glad to hear that your issue has been resolved by reverting Classic Outlook to an older version. This is a very helpful insight and can certainly support other users who may encounter the same behavior.

You may also consider sharing this issue on the Outlook · Community. This is the official channel for reporting unexpected behavior, and it ensures that your feedback reaches Microsoft’s development team, helping them stay aware of the issue and work on potential fixes in a future update.

Your feedback is valuable and truly appreciated.

Thank you again for your time and your contribution.

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Outlook Classic (MS 365, Exchange) calendar attachments not visible to other users

1 answer

Your answer