Helpful Exchange Online Powershell commands
Find all mailboxes and users with full access.
Get-Mailbox -resultsize "Unlimited" | Get-MailboxPermission | where { ($_.AccessRights -eq "FullAccess") -and ($_.IsInherited -eq $false) -and -not ($_.User -like "NT AUTHORITY\SELF") } | ft @{Name="Identity";expression={($_.Identity -split "/")[-1]}}, User -AutoSize > mailboxes.csv