如何在C#中不使用本地文件系统添加Azure Blob文件作为邮件附件？

完全可以实现，核心思路是直接读取Azure Blob的数据流，将其作为邮件附件的数据源，不需要把文件下载到本地磁盘。以下是具体实现方案：

依赖准备 #

需要安装两个核心NuGet包：

• Azure Blob存储操作：Azure.Storage.Blobs
• 邮件发送库（推荐更现代的MailKit，兼容.NET所有版本）：MailKit

实现代码（MailKit版本） #

using Azure.Storage.Blobs;
using MailKit.Net.Smtp;
using MimeKit;
using System.IO;

public async Task SendEmailWithBlobAttachmentAsync(
    string blobConnectionString, 
    string containerName, 
    string blobName, 
    string smtpServer, 
    int smtpPort, 
    string smtpUser, 
    string smtpPassword, 
    string toEmail, 
    string subject, 
    string body)
{
    // 1. 获取Blob的只读数据流
    var blobServiceClient = new BlobServiceClient(blobConnectionString);
    var blobContainerClient = blobServiceClient.GetBlobContainerClient(containerName);
    var blobClient = blobContainerClient.GetBlobClient(blobName);

    using var blobStream = await blobClient.OpenReadAsync();
    var blobProps = await blobClient.GetPropertiesAsync();

    // 2. 构建邮件及附件
    var message = new MimeMessage();
    message.From.Add(new MailboxAddress("发送方", smtpUser));
    message.To.Add(new MailboxAddress("接收方", toEmail));
    message.Subject = subject;

    var bodyBuilder = new BodyBuilder();
    bodyBuilder.TextBody = body;
    // 直接将Blob流作为附件传入，自动获取文件的MIME类型
    bodyBuilder.Attachments.Add(blobName, blobStream, ContentType.Parse(blobProps.Value.ContentType));

    message.Body = bodyBuilder.ToMessageBody();

    // 3. 发送邮件
    using var smtpClient = new SmtpClient();
    await smtpClient.ConnectAsync(smtpServer, smtpPort, MailKit.Security.SecureSocketOptions.StartTls);
    await smtpClient.AuthenticateAsync(smtpUser, smtpPassword);
    await smtpClient.SendAsync(message);
    await smtpClient.DisconnectAsync(true);
}

备选方案（System.Net.Mail版本，适用于.NET Framework或兼容场景） #

using Azure.Storage.Blobs;
using System.Net;
using System.Net.Mail;
using System.IO;

public async Task SendEmailWithBlobAttachmentNetMailAsync(
    string blobConnectionString, 
    string containerName, 
    string blobName, 
    string smtpServer, 
    int smtpPort, 
    string smtpUser, 
    string smtpPassword, 
    string toEmail, 
    string subject, 
    string body)
{
    var blobServiceClient = new BlobServiceClient(blobConnectionString);
    var blobContainerClient = blobServiceClient.GetBlobContainerClient(containerName);
    var blobClient = blobContainerClient.GetBlobClient(blobName);

    using var blobStream = await blobClient.OpenReadAsync();
    var blobProps = await blobClient.GetPropertiesAsync();

    // 创建附件时直接传入Blob流
    var attachment = new Attachment(blobStream, blobName, blobProps.Value.ContentType);

    var mailMessage = new MailMessage();
    mailMessage.From = new MailAddress(smtpUser);
    mailMessage.To.Add(toEmail);
    mailMessage.Subject = subject;
    mailMessage.Body = body;
    mailMessage.Attachments.Add(attachment);

    using var smtpClient = new SmtpClient(smtpServer, smtpPort)
    {
        Credentials = new NetworkCredential(smtpUser, smtpPassword),
        EnableSsl = true
    };
    await smtpClient.SendMailAsync(mailMessage);
}

关键注意事项 #

• 权限验证：确保Blob客户端拥有Blob的读取权限，可以通过连接字符串、SAS令牌或Azure AD身份验证实现。
• 资源释放：使用using语句包裹Blob流，确保数据流使用后自动释放，避免内存泄漏。
• 大文件支持：流式处理无需将整个文件加载到内存，适合大文件场景。

内容的提问来源于stack exchange，提问作者AZ Chad