Use this parameter to remove the Send As permission to the mailbox specified by the Identity parameter from the user specified ...

Use this parameter to remove the Send As  permission to the mailbox specified by the Identity parameter from the user specified by the TrustedUser parameter. This parameter accepts the arguments True or False. These arguments are not case sensitive. When using a CSV file, specify RemoveSendAs True to remove the permission or RemoveSendAs False to not remove the permission. Specifying False will not add the permission if it is already set. To add the permission, use Add-MSOnlineMailPermission.