Microsoft Graph 5.17（C#）添加附件发邮件抛出ODataError求助

我在使用Microsoft Graph 5.17版本的C#代码发送邮件时，发现不添加附件可以正常发送，但添加附件后会抛出Microsoft.Graph.Models.ODataErrors.ODataError异常。以下是我的代码片段：

string tenantId = "";
string clientId = "";
string clientSecret = "";
string sMailboxUserObjectId = "";

var message = new Message();
List<Recipient> recLst = new List<Recipient>();
List<string> ToLst = new List<string>();
ToLst.Add("someone@gmail.com");
foreach (var recipient in ToLst)
{
    Recipient recObj = new Recipient();
    EmailAddress emailObj = new EmailAddress();
    emailObj.Address = recipient;
    recObj.EmailAddress = emailObj;
    recLst.Add(recObj);
}
message.ToRecipients = new List<Recipient>(recLst);

message.Body = new ItemBody
{
    //ContentType = BodyType.Html,
    Content = "Test mail, please ignore"
};

message.Subject = "Test Mail. ";
var att1 = new MG.Models.Attachment
{
    Name = "PoweredOffMachines_2023_7_18_9.csv",
    ContentType = "text/csv",
    OdataType = "#microsoft.graph.fileAttachment",
    Id = "PoweredOffMachines_2023_7_18_9",  
};

message.Attachments = new List<MG.Models.Attachment>();
message.HasAttachments = true;
message.Attachments.Add(att1);

var saveToSentItems = false;

SendMailPostRequestBody sendMailReqBody = new SendMailPostRequestBody();
sendMailReqBody.Message = message;
sendMailReqBody.SaveToSentItems = saveToSentItems;

try
{
    var scopes = new[] { "https://graph.microsoft.com/.default" };
    var clientSecretCredential = new ClientSecretCredential(
        tenantId, clientId, clientSecret);
    var graphClient = new MG.GraphServiceClient(clientSecretCredential, scopes);

    await graphClient
        .Users[sMailboxUserObjectId]
        .SendMail
        .PostAsync(sendMailReqBody);

}
catch (Exception ex)
{
    return "Failure";
}

问题原因 #

你的代码在创建fileAttachment时存在两个致命问题：

1. 未提供附件内容：#microsoft.graph.fileAttachment类型必须包含文件的实际内容，要么通过ContentBytes传入Base64编码的字节数组，要么通过ContentUrl传入可访问的文件链接，缺少内容会导致Graph API拒绝请求并抛出ODataError。
2. 手动设置附件Id：附件的Id是由Graph API自动生成的，不需要手动指定，手动设置可能引发数据冲突。

修复方案 #

修改附件创建部分，添加文件内容的Base64编码，并移除手动设置的Id属性：

// 读取本地文件并转换为Base64编码
string filePath = @"C:\Your\File\Path\PoweredOffMachines_2023_7_18_9.csv";
byte[] fileContent = File.ReadAllBytes(filePath);
string base64Content = Convert.ToBase64String(fileContent);

var att1 = new MG.Models.Attachment
{
    Name = "PoweredOffMachines_2023_7_18_9.csv",
    ContentType = "text/csv",
    OdataType = "#microsoft.graph.fileAttachment",
    ContentBytes = base64Content // 新增：传入文件的Base64内容
    // 移除手动设置的Id属性
};

额外注意事项 #

• 确保应用拥有读取目标文件的权限，若文件来自网络存储，需保证能获取到字节内容。
• 若使用ContentUrl替代ContentBytes，需确保该URL对Graph API是可访问的（例如公开链接或带有效凭证的链接）。
• 确认应用已配置正确的权限：发送邮件需拥有Mail.Send应用权限（已在你的代码中使用.default范围，需确保权限已在Azure AD中授予）。

内容的提问来源于stack exchange，提问作者Venkata Praveen