Register your app in the Microsoft Entra admin center .
using Microsoft.Graph; using Azure.Identity; var scopes = new[] { "https://microsoft.com" }; var options = new ClientSecretCredentialOptions { AuthorityHost = AzureAuthorityHosts.AzurePublicCloud, }; var clientSecretCredential = new ClientSecretCredential( tenantId, clientId, clientSecret, options); var graphClient = new GraphServiceClient(clientSecretCredential, scopes); Use code with caution. 3. Locating the Message and Attachments Register your app in the Microsoft Entra admin center
To interact with the API, you first need to authenticate. For background services (daemons), use the credential. Locating the Message and Attachments To interact with
Attachments are nested under a specific message. You first need the MessageId . You can find this by listing messages in a user's inbox: You first need the MessageId
var messageId = "YOUR_MESSAGE_ID"; var userId = "user@example.com"; // Fetch all attachments for the message var attachments = await graphClient.Users[userId] .Messages[messageId] .Attachments .GetAsync(); foreach (var attachment in attachments.Value) { // Check if it's a file attachment if (attachment is FileAttachment fileAttachment) { string fileName = fileAttachment.Name; byte[] contentBytes = fileAttachment.ContentBytes; // Save to local path string folderPath = @"C:\Downloads\Attachments"; File.WriteAllBytes(Path.Combine(folderPath, fileName), contentBytes); Console.WriteLine($"Downloaded: {fileName}"); } } Use code with caution. 5. Handling Large Attachments
var messages = await graphClient.Users["user@example.com"].Messages .GetAsync(config => { config.QueryParameters.Filter = "hasAttachments eq true"; config.QueryParameters.Select = new[] { "id", "subject" }; }); Use code with caution. 4. Downloading the Attachment Content
You’ll need Mail.Read or Mail.ReadWrite permissions. NuGet Packages: Install the following packages: Microsoft.Graph Azure.Identity (for authentication) 2. Authenticating the Graph Client