How to grant a single user access to access all users calendars Office 365 PowerShell

Open Power Shell as an Administrator

Go to Start
Search for Power Shell
Right click on Windows Power Shell
Run as Administrator

Run the following commands

Set-ExecutionPolicy RemoteSigned

(Need to configure this setting only once on your computer)
-Press “A” or “Y”
–Press Enter

 $UserCredential = Get-Credential

Windows Power Shell Credential Request
Enter Admin’s Username & Password

 $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection

 Import-PSSession $Session -DisableNameChecking

The various levels of permissions are as follows:

• None – Has no access to the folder.
• Owner – Gives full control of the folder. An Owner can create, modify, delete, and read folder items; create sub folders; and change permissions on the folder.
• Publishing Editor – Has all rights granted to an Owner, except the right to change permissions. A Publishing Editor can create, modify, delete, and read folder items and create sub folders.
• Editor – Has all rights granted to a Publishing Editor, except the right to create subfolders. An Editor can create, modify, delete, and read folder items.
• Publishing Author – Can create and read folder items and create subfolders but can modify and delete only folder items that he or she creates, not items created by other users.
• Author – Has all rights granted to a Publishing Author but cannot create subfolders. An Author can create and read folder items and modify and delete items that he or she creates.
• Nonediting Author – Can create and read folder items but cannot modify or delete any items, including those that he or she creates.
• Reviewer – Can read folder items but nothing else.
• Contributor – Can create only folder items and cannot read items.
• Availability Only – View only availability data
• Limited Details – View availability data with subject and location

Select the Permission Level

 $userToAdd = "user@yourdomain.com"
 $users = Get-Mailbox | Select -ExpandProperty PrimarySmtpAddress
 Foreach ($u in $users)
 {
 $ExistingPermission = Get-MailboxFolderPermission -Identity $u":\calendar" -User $userToAdd -EA SilentlyContinue
 if ($ExistingPermission) {Remove-MailboxFolderPermission -Identity $u":\calendar" -User $userToAdd -Confirm:$False}
 if ($u -ne $userToAdd) {Add-MailboxFolderPermission $u":\Calendar" -user $userToAdd -accessrights Owner}
 }

Replace the “Owner” with the Permission level you wanna select