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When sharing a document the sharing box look like this:
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The user is able to change the way the document is shared:
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When sharing in this manner, the inheritance will break.
You can prevent users with members permissions to break inheritance by doing the following:
Go to Site Settings à -> Site Permissions à -> Access Request Settings
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By removing the checkmark for “Allow members to share the site and individual files and folders” ordinary users will be prevented from breaking inheritance anywhere on the site.
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The sharing box will look like this:
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If the user tries to manually add an email address of an external user the following error page appears:
Changing default settings for sharing
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In SharePoint Admin Center chose Sites à -> Active sites à -> The site to change à -> Settings à More sharing settings
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Default sharing link type is usually set to “Anyone with the link”.
Remove the checkmark and choose “People with existing access” and Save.
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With this setting the inheritance will not break as the sharing will be with users that already have access and no change in permissions is necessary.
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