"To use this mailbox, you have to be able to edit this site" message when you browse to a site mailbox from SharePoint Online in Office 365

PROBLEM

As a site collection administrator in Microsoft SharePoint Online, you click the option to create a new site mailbox. When you browse to the site mailbox, you receive the following message:
Almost there!

To use this mailbox, you have to be able to edit this site. If you were just invited to edit, try again in 15 minutes.

SOLUTION

To fix this issue, add the affected user to the Owners group or to the Members group for the site collection or subsite. To do this, follow these steps:
  1. Browse to the site or site collection where you created the site mailbox.
  2. Click the gear icon for the Settings menu, and then click Site settings.
  3. Click Site permissions.
  4. On the ribbon, click Grant Permissions.
  5. Click SHOW OPTIONS, select the Members or Owners group permission level, enter the name of the affected user, and then click Share.
Note These permissions must be assigned even though the affected user is a site collection administrator.

MORE INFORMATION

This issue occurs because a user must exist in the Owners group or the Members group for the site collection or subsite to be able to access the site mailbox for that site, even if the user is a site collection administrator.

For more information, go to the following Microsoft website:

Still need help? Go to Microsoft Community.
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Article ID: 3069134 - Last Review: Dec 21, 2016 - Revision: 1

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