Outlook doesn't manage like Excel. Everyone can open the same item at the
same time. If multiple people make changes, of course, you may get a warning
about conflicts.

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Sue Mosher, Outlook MVP
Author of
Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> How many people can access the public outlook contacts
> folder at the same time? For example, there are 5 people
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> to open the same excel spread sheet, one person can only
> see it as a read-only file.