Email 从本地外汇账户发送时“5.7.1无法中继”

我有一个程序，它试图使用内部Exchange帐户向外部地址发送电子邮件，我收到以下错误：

邮箱不可用。服务器响应为5.7.1无法中继

我们有Exchange 2010。我不明白为什么，因为我用来发送的帐户是本地帐户。这是我的密码：

Dim client As SmtpClient = New SmtpClient("webmail.company.com") 
client.DeliveryMethod = SmtpDeliveryMethod.Network
client.UseDefaultCredentials = False
client.Credentials = New NetworkCredential("Service", "pwd", "company")
Dim message As MailMessage = New MailMessage("service@company.com", "someone@outsidecompany.com")
Message.Body = "Test Message"
Message.Subject = "Hello"
client.Send(message)
message = Nothing

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您需要在smtp接收连接器上授权exchange上的用户向公司外部发送：

Get-ReceiveConnector "Default SMTP" | Add-ADPermission -User "COMPANY\Service" -ExtendedRights "ms-Exch-SMTP-Accept-Any-Recipient"