Initial commit: WpywMail 自建邮件系统：.NET 8 原生 SMTP/IMAP 服务端（DKIM 签名、SPF/DKIM/DMARC 入站校验、SQLite 存储、完整账号体系）、Node 服务端、WinUI 3 客户端与 Web 前端

2026-09-19 11:19:40 +08:00
commit b8814a7615
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+namespace WpywMail.Native;
+
+/// <summary>
+/// 发件队列。轮询待发任务 → 读取原始报文 →（可选）DKIM 签名 → 投递 → 记录结果。
+///
+/// 相比 v1 的改进：
+///  1. 重试策略可配置（4xx 与 5xx 分开处理，指数退避带上限）；
+///  2. DKIM 在投递时签名，因此每次重试都会带上新的时间戳；
+///  3. 彻底失败时给发件人投递一封退信（NDR），不再静默丢失。
+/// </summary>
+public sealed class DeliveryQueue
+{
+    private readonly AppConfig config;
+    private readonly IMailStore store;
+    private readonly DirectSmtpDelivery delivery;
+    private readonly DkimSigner? signer;
+
+    public DeliveryQueue(AppConfig config, IMailStore store, DkimSigner? signer)
+    {
+        this.config = config;
+        this.store = store;
+        this.signer = signer;
+        delivery = new DirectSmtpDelivery(config, store);
+    }
+
+    public async Task RunAsync(CancellationToken token)
+    {
+        AppLog.Info($"[发送] 投递模式：{(config.DeliveryMode.Equals("relay", StringComparison.OrdinalIgnoreCase) ? "SMTP 中继" : "按 MX 直接投递")}");
+        AppLog.Info($"[发送] 重试策略：最多 {config.Retry.MaxAttempts} 次，初始间隔 {config.Retry.InitialDelaySeconds}s，上限 {config.Retry.MaxDelaySeconds}s" +
+                    (config.Retry.RetryOnPermanentFailure ? $"，5xx 也重试 {config.Retry.MaxAttemptsForPermanent} 次" : "，5xx 视为永久失败"));
+
+        while (!token.IsCancellationRequested)
+        {
+            foreach (var job in store.TakeDueQueue(10))
+            {
+                if (token.IsCancellationRequested) break;
+                await ProcessAsync(job, token);
+            }
+            try { await Task.Delay(TimeSpan.FromSeconds(5), token); }
+            catch (OperationCanceledException) { break; }
+        }
+    }
+
+    private async Task ProcessAsync(QueueItem job, CancellationToken token)
+    {
+        var targets = string.Join(", ", job.Recipients);
+        try
+        {
+            var message = store.GetById(job.MessageId) ?? throw new InvalidOperationException("发送队列中的邮件不存在。");
+
+            // 每次投递都重新读取原始报文。
+            // 关键顺序：先把行尾规范化为 CRLF，再签名 —— 这样签名覆盖的字节
+            // 与传输时写出的字节完全一致（传输阶段只做 dot-stuffing）。
+            var raw = SmtpDataEncoder.Normalize(store.ReadRaw(message.RawPath));
+            if (signer is not null)
+            {
+                raw = signer.Sign(raw);
+                message.DkimSigned = true;
+            }
+
+            await delivery.DeliverAsync(message, job.Recipients, raw, token);
+            store.CompleteQueue(job);
+            AppLog.Info($"[发送] 投递成功：{targets}（第 {job.Attempts + 1} 次尝试）");
+        }
+        catch (Exception ex)
+        {
+            store.FailQueue(job, ex, config.Retry, out var gaveUp);
+            if (gaveUp)
+            {
+                AppLog.Error($"[发送] 已放弃投递：{targets} —— {ex.Message}");
+                if (config.Retry.SendBounceNotification) SendBounce(job, ex);
+            }
+            else
+            {
+                AppLog.Warn($"[发送] 投递失败（将重试）：{targets} —— {ex.Message}");
+            }
+        }
+    }
+
+    private void SendBounce(QueueItem job, Exception error)
+    {
+        try
+        {
+            var message = store.GetById(job.MessageId);
+            if (message is null) return;
+            store.CreateBounce(job.OwnerEmail, message.Subject, job.Recipients, error.Message, message.RawPath);
+            AppLog.Info($"[发送] 已向 {job.OwnerEmail} 投递退信通知。");
+        }
+        catch (Exception ex)
+        {
+            AppLog.Error($"[发送] 生成退信失败：{ex.Message}");
+        }
+    }
+}