List mailboxes with Full Access permissions assigned

You can use PowerShell to produce a list of all mailboxes that have Full Access permissions assigned against them, including who has the permission set:

Get-Mailbox | Get-MailboxPermission | where { ($_.AccessRights -eq “FullAccess”) -and ($_.IsInherited -eq $false) -and -not ($_.User -like “NT AUTHORITY\SELF”) } | Select-Object Identity,User | export-csv C:\Temp\FullAccess.csv

Note that any mailbox that doesn’t have additional Full Access permissions defined (e.g. those where only the user associated with the mailbox has access) will not be included.