VB.Net调用Microsoft Graph SendMail返回ErrorInternalServerError如何解决？

错误触发核心原因 #

你在构造邮件收件人列表时错误使用了仅适用于日历事件的Attendee类型填充ToRecipients字段，邮件的ToRecipients集合要求接收的是Recipient类型实例，Attendee额外携带的Type属性在邮件发送接口的校验逻辑中无法被识别，最终触发服务端内部错误。

修复方案 #

1. 修正收件人构造逻辑 #

修改DefineImportantEmail方法，将Attendee替换为标准Recipient类型，删除不相关的Type属性赋值：

Function DefineImportantEmail(Locations As String, Recipients As List(Of (String, String))) As Message
    Dim title = "IMPORTANT OUTAGE NOTIFICATION"
    Dim message = "Outage at " & Locations

    Dim RecipientList = New List(Of Recipient)
    For Each recipient In Recipients
        RecipientList.Add(New Recipient With {
                .EmailAddress = New EmailAddress With {
                    .Address = recipient.Item1,
                    .Name = recipient.Item2
                }
            })
    Next

    Return New Message With {
        .Subject = title,
        .Body = New ItemBody With {
            .ContentType = BodyType.Text,
            .Content = message
        },
        .ToRecipients = RecipientList
    }
End Function

2. 可选优化&兜底排查 #

如果修改类型后仍存在异常，可按以下顺序排查：

• 确认Azure中配置的Mail.Send权限已完成管理员同意，权限类型和你的认证逻辑匹配：客户端凭证流使用应用权限，用户登录流使用委托权限
• 确认发件人邮箱账号未被组织限制发送权限，可通过OWA手动登录该账号发送测试邮件验证
• 避免使用Wait()同步调用异步方法，改为Await调用防止线程死锁引发额外异常，优化后的发送代码参考：

Async Function SendImportantEmail(Locations As String, Recipients As List(Of (String, String))) As Task
    Dim SaveToSentItems = True
    Dim graphClient = GetGraphClient()
    Dim EventObject = DefineImportantEmail(Locations, Recipients)
    Await graphClient.Users("xxxxx@xxxxxxxxxxxxxxx.com").SendMail(EventObject, SaveToSentItems).Request().PostAsync()
End Function

内容的提问来源于stack exchange，提问作者Close to the Wheels