Outlook calendar

Question

I need help with our Calendar. We have too much old data that our IT department cant get rid of so we would like to either start a new 2nd calendar or be able to delete some old data. I cant loose the information that we already have on file now. Typically when I drag something onto someone calendar its giving me this message below. We use this for our scheduling system.

Answer 1

Hi @Angela Breslin,

Thank you for your response.

Certainly, creating a new calendar while keeping the existing one available for reference is absolutely a valid and commonly used approach. Many organizations do this when a shared calendar becomes difficult to manage due to legacy users or outdated configuration.

Below are a couple of options you may want to consider:

 

Option 1 (Quickest): Create a new shared calendar and keep the current one for reference

You can create an additional calendar in Outlook and begin using it going forward, while keeping the existing calendar as read‑only or for historical reference.

Steps for New Outlook / Outlook on the web:

1. Go to Calendar
2. Select Add calendar
3. Choose Create blank calendar
4. Name it (for example, Installer Schedule – New)
5. Save the calendar and share it with the current installers or schedulers, granting Can edit permissions as needed

Important notes:

If the new calendar is created as a secondary calendar under a user’s mailbox, Outlook has some built‑in limitations:

• Events on secondary calendars don’t contribute to Free/Busy availability in Scheduling Assistant
• Some meeting responses and notifications may behave differently compared to a primary calendar

For more detail steps, please refer to: Create additional calendars - Microsoft Support.

 

Option 2 (Best long‑term approach): Use a Microsoft 365 Group calendar

If this calendar is intended for a team (installers and schedulers), a Microsoft 365 Group may be a better long‑term option:

• Each group includes a shared calendar by default
• Membership controls access automatically as users join or leave
• It simplifies ongoing permission management and reduces clutter over time

Reference: Use a Group calendar in Outlook to schedule and edit events - Microsoft ...

 

Additional note on performance:

If Outlook performance is part of the issue, it’s also worth noting that Outlook can slow down when users have many shared calendars or mailboxes added, especially during synchronization. Even if the issue seems tied to one calendar, the overall number of shared resources can contribute to performance degradation.

Reference: Outlook performance issues when you have many shared folders or ...

 

Please feel free to reach out if you have any questions or need further clarification.

If you found the response helpful, I’d greatly appreciate it if you could mark it as accepted. This helps surface the solution for others who may be experiencing a similar issue and supports the broader community by making useful guidance easier to find.

Thank you for your time and collaboration.

Warm regards.

Answer 2

Hi @Angela Breslin,

Good day, and I appreciate the clear explanation of your concern.  

I understand the challenge you’re experiencing with your Outlook calendar - especially when it’s used as a scheduling system and contains a large amount of historical data that can’t be removed without risking data loss.

Below is a practical approach you can try to preserve your historical data while restoring reliable scheduling functionality:

1/ Create a second (new) calendar in Outlook on the web (Business)

This is the cleanest and most supported way to effectively “start fresh” while keeping the existing calendar for historical reference.

• Open Outlook on the web and go to Calendar
• In the left pane, select Add calendar
• Choose Create blank calendar
• Assign a name (for example, Scheduling – 2026), select a color or icon, choose a group if desired, and click Save.

Optional – Share with schedulers:

• Next to the new calendar, select More (⋯) > Sharing and permissions
• Add users and assign appropriate permissions (typically Can edit)

Reference: Add a calendar in Outlook on the web - Microsoft Support.

 

 

 

 

2/ Treat the existing calendar as “historical” (hide, don’t delete)

After creating the new calendar:

• Uncheck the old calendar in the left pane to keep it out of daily scheduling
• Re‑enable it anytime for reference or lookup purposes

While this won’t immediately reduce mailbox size, it significantly improves usability and performance for active scheduling.

 

3/ Reduce mailbox size without losing historical data

If the goal is also to reduce the size of the active mailbox, here are safe options:

Option A: Manual archive to a PST (Classic Outlook for Windows)

If your organization allows PST archiving:

• Open Classic Outlook for Windows
• Go to File > Info > Tools / Cleanup Tools > Archive
• Select Archive this folder and all subfolders
• Choose Calendar
• Set a cutoff date (for example, archive items older than 1–2 years)
• Select a PST file location and run the archive

Note: This option may be disabled or overridden by organizational retention policies.

Reference: Archive items manually - Microsoft Support.

 

Option B: IT‑managed Online Archive (best long‑term approach)

If you’re using Exchange Online, IT can:

• Enable an Archive Mailbox
• Apply retention tags or policies that automatically move older calendar items to the archive

This keeps historical data accessible while reducing the size of the primary mailbox.

Reference: Customize an archive and deletion policy (MRM) for mailboxes.

 

4/ About the drag‑and‑drop error (“lost due to a reconnect with the server”)

This error typically indicates a temporary loss of synchronization or a shared calendar feature conflict.

To help narrow this down, please confirm whether the issue occurs in Outlook on the web, the Classic Outlook desktop app, or New Outlook.

If the issue occurs in Classic Outlook for Windows, please try the following:

a. Ensure Outlook is fully updated

b. Disable Shared Calendar Improvements

This setting is a known cause of drag‑and‑drop issues in some environments.

• Outlook > File > Account Settings > Account Settings
• Double‑click your account > More Settings
• On the Advanced tab, uncheck Turn on Shared Calendar Improvements
• Restart Outlook

c. Test Outlook in Safe Mode

This helps rule out add‑ins:

outlook.exe /safe

Then test drag‑and‑drop again.

d. Create a new Outlook profile

• Control Panel > Mail > Show Profiles > Add
• Re‑add your account and test again

 

I hope this information helps. Please try these steps and let me know if they resolve the issue. If the problem persists, I’ll be happy to continue working with you to find the most suitable solution.

As other users will also search for information in this community, your vote can significantly help those with similar inquiries quickly locate the most relevant resources. 

Thank you for your kindness and for contributing to the forum.   

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Answer 3

For the two separate needs (freeing space without losing data, and fixing the drag‑and‑drop error), use different approaches.

1. Reduce old calendar data without losing it

Since the existing calendar must be preserved, archive old items instead of deleting them permanently.

In classic Outlook for Windows (connected to Exchange/Microsoft 365):

1. On the File tab, select Cleanup Tools > Archive.
2. Select Archive this folder and all subfolders.
3. In the folder list, select Calendar.
4. In Archive items older than, choose a cutoff date (for example, archive everything older than 1–2 years).
5. Optionally select Include items with "Do not AutoArchive" checked to ensure everything older than that date is archived.
6. Choose or confirm the Outlook Data File (.pst) location where the archive will be stored and select OK.

This moves older calendar items into a separate PST file while keeping them accessible if needed, and reduces the size of the active calendar/mailbox.

If the organization has disabled PST/Archive creation, IT must enable it or use server‑side tools/retention policies to move or delete old calendar items.

2. Starting a second calendar

If the goal is to keep the existing calendar as historical data and schedule only new work on a fresh calendar, create an additional calendar instead of clearing the old one. (Creation steps are not in the provided context, but this is fully supported in Outlook/OWA.) The original calendar can then be archived as above to keep mailbox size under control.

3. Error when dragging items between calendars

The dialog in the screenshot:

Cannot copy the items. Changes made to the item were lost due to a reconnect with the server.

is typically caused by sync or corruption issues with calendar items.

If specific items cannot be deleted or moved and reappear or fail to copy, they may be corrupted. For such items in an Exchange mailbox:

1. Have IT run the following Exchange PowerShell cmdlet on the affected mailbox:

      Set-Mailbox <name_of_affected_mailbox> -CalendarVersionStoreDisabled $true
   

2. Wait about two hours for the store configuration cache to expire (or, for on‑premises Exchange only, restart the Information Store service or move the database to another Exchange server, understanding this causes a service interruption).
3. After that, delete the problematic calendar item(s). Using the MFCMAPI tool is recommended for stubborn/corrupted entries.
4. When finished, re‑enable calendar logging:

      Set-Mailbox <name_of_affected_mailbox> -CalendarVersionStoreDisabled $false
   

This procedure is for IT/admins and should not be run by end users without proper permissions and change control.

For general sync issues (not specific corrupted items), IT can also clear and resync the local calendar cache on affected desktops by using Clear Offline Items on the Calendar folder, or by recreating the Outlook profile, so that Outlook downloads a clean copy of the calendar from the server.

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References:

• Can't delete calendar items in Outlook
• Remove items from your calendar
• Outlook shows conflict errors when updating or cancelling meetings