Calendar Outlook

Dear Marco,

There is no fixed limit that applies to every machine, but opening a large number of shared calendars is a recognized cause of errors and slow performance. Microsoft notes that a computer with slower hardware, a large mailbox, and a slow network may struggle beyond five shared folders or mailboxes, while a faster machine with a smaller mailbox may handle ten or more. I tried to replicate this on my side and was able to open around ten shared calendars without any trouble. It suggests the threshold here is tied to her machine, mailbox size, or network rather than a hard limit in Outlook, so it is worth looking at what is different about her setup.

1. Close all shared calendars.
2. Restart Outlook.
3. Open only three to five shared calendars.
4. Add the remaining calendars gradually until the problem returns.
5. Record whether one particular calendar consistently causes the warning.

If a specific calendar fails even when opened alone, your IT administrator should check the secretary’s permissions for that calendar.

For practical daily use, the most reliable approach is keeping only the calendars needed for the current task ticked rather than loading all of them at once.

I hope this helps. Looking forward to your reply.

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