Dear: 有一客戶要寄到Office 365的群組信箱, 被退信, 退信訊息如下 A communication failure occurred during the delivery of your message. Please try resending the message later. For more tips to help resolve this issue, see DSN code 5.4.1 in Exchange Online - Office 365 . If the problem continues, contact your email admin 請問是對方被對垃圾郵件嗎
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