Yesterday I had to add all licensed users to a Mail Enabled Security Group and then add that group to Room, Equipment and user mailboxes with desired permissions.

To add all Licensed users to a group:

$users = Get-MsolUser | Where-Object { $_.isLicensed -eq "TRUE" }

$users | foreach {Add-DistributionGroupMember -identity Mail_Enabled_Security_Group -Member $_.userprincipalname}

Give permissions to:

$allmailbox = Get-Mailbox -Resultsize Unlimited -Filter {RecipientTypeDetails -eq 'Type_Of_Mailbox_You_Want'}

Foreach ($Mailbox in $allmailbox)
{
    $path = $Mailbox.alias + ":" + (Get-MailboxFolderStatistics $Mailbox.alias | Where-Object { $_.Foldertype -eq "Calendar" } | Select-Object -First 1).Name
    set-mailboxfolderpermission –identity ($path) –user Mail_Enabled_Security_Group -Member –Accessrights Right_You_Want_To_Add
} 

Available permissions are:

Owner, PublishingEditor, Editor, PublishingAuthor, Author, NonEditingAuthor, Reviewer, Contributor, AvailabilityOnly, LimitedDetails

Available RecipientTypeDetails are:

UserMailbox, RoomMailbox, EquipmentMailbox

That all. Powershell rocks again :)

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