Дайте вывод команды:
get-mailbox -arbitration | select name,ProhibitSendQuota
>get-mailbox -arbitration | select name,ProhibitSendQuota
Name ProhibitSendQuota
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Migration.8f3e7716-2011-43e4-96b1-aba62d229136 300 MB (314,572,800 bytes)
FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042 1 MB (1,048,576 bytes)
SystemMailbox{bb558c35-97f1-4cb9-8ff7-d53741dc928c} Unlimited
SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9} Unlimited