How to transfer historical outlook events/appointments to a shared calendar

Question

How to transfer historical outlook events/appointments to a shared calendar

Becerra, Chris 0

I have a user who has over 3,000 appointments in his outlook calendar and I need to transfer/copy those appointments to a shared calendar within a shared mailbox I've created. Every time I go into View -Listed - set a date range of a year, and start the copy, I keep getting a message stating: This function cannot be performed because the message has been changed.

I have made myself "Delegate" of User A's account, I have the Outlook client open with User A's email account, and I've also made User A delegate of Shared Mailbox.

Becerra, Chris 0 Reputation points

2026-04-29T18:48:04.5533333+00:00

Just to confirm, the ics import will NOT send "updates" out to the users, will it?
Gabriel-N 16,475 Reputation points Microsoft External Staff Moderator

2026-05-01T06:34:41.43+00:00

Hello Becerra, Chris

Sorry for late reply. Importing an .ics file will not send any updates or notifications to other users.

When you import an .ics file, Outlook simply adds the events to your calendar as local items. It does not treat them as active meeting requests or trigger any emails to attendees.

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Becerra, Chris 0 Reputation points

2026-04-29T18:48:04.5533333+00:00

Just to confirm, the ics import will NOT send "updates" out to the users, will it?
Gabriel-N 16,475 Reputation points Microsoft External Staff Moderator

2026-05-01T06:34:41.43+00:00

Hello Becerra, Chris

Sorry for late reply. Importing an .ics file will not send any updates or notifications to other users.

When you import an .ics file, Outlook simply adds the events to your calendar as local items. It does not treat them as active meeting requests or trigger any emails to attendees.

Answer 1

Hello Becerra, Chris

Thank you for sharing the details.

While testing on my side, I was able to reproduce the same error (“This function cannot be performed because the message has been changed”) when copying large numbers of appointments. This typically occurs due to synchronization conflicts between Outlook’s local cache and the Exchange server during bulk operations.

To work around this, you may want to try an alternative approach instead of copying directly:

First, export User A’s calendar to an .ics file
Then, add the shared mailbox as a full account in Outlook (not just as an additional/shared mailbox)
Make sure the shared mailbox calendar is set as the default during the import process
After that, import the .ics file

When prompted to choose between Open or Import, select Import. The appointments will then be added to the shared mailbox calendar and begin syncing as expected

User's image

Hope this helps, and please feel free to share any updates from your side.

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How to transfer historical outlook events/appointments to a shared calendar

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