param(
    $mailbox,
    $user
)

Add-MailboxPermission -Identity $mailbox -User $user -AccessRights Full
Add-RecipientPermission -Identity $mailbox -Trustee $user -AccessRights SendAs -Confirm $false

"Access Permissions:" | Out-Host
Get-Mailbox $mailbox | Get-MailboxPermission | Format-Table
"Sending Permissions:" | Out-Host
Get-RecipientPermission -Identity $mailbox | Format-Table