Get-<Command> -<noun> <MailboxPermission>

Get-MailboxPermission

Get-MailBoxPermission -Identity *

Get-MailboxPermission -Identity office.onmicrosoft.com\office

Get-MailboxPermission -Identity office.onmicrosoft.com\office -user Tom

myfirst@mydom.com,mysecond@mydom.com, mythird@mydom.com | Get-MailboxPermissions

Add-MailboxPermission -Identity jane -User tom -AccessRights ReadItems

Add-MailboxPermission -Identity jane -Owner tom

Get-Mailbox -ResultSize unlimited -Filter {(RecipientTypeDetails -eq 'UserMailbox')} | Add-MailboxPermission -User tom@mydom.com -AccessRights fullaccess -InheritanceType all

Add-MailboxFolderPermission -Identity jane:\Sales -User tom -AccessRights Owner

Remove-MailboxPermission -identity jane -User tom -AccessRights full-access -InheritanceType all

identity,user,right,inheritance
"Tom Meier",jerry@mydom.com,FullAccess,All
Conferenceroom,tom,ReadItems,All
[...]

If (test-Path (PathtoCsvFile)){$ValuesField = import-csv PathtoCSVFile; }
Else {write-Host "Unfortunately the file was not found!" -foregroundColor "red"; Exit 1;}

Function validateUser ($ExObj){
  If (Get-user -Identity $ExObj -EA SilentlyContinue) {
    Return $TRUE;}
  Else {Return $FALSE}}