Added _fetchClient.NoOpAsync() to re-sync with the idle client.

Author: danzuep

samples/WorkerServiceExample/Worker.cs

@@ -33,17 +33,26 @@ protected override async Task ExecuteAsync(CancellationToken cancellationToken =
 
     private async Task NotReentrantAsync(CancellationToken cancellationToken = default)
     {
+        var sendTask = DelayedSendAsync(5, cancellationToken);
+
+        var newestEmail = await GetNewestMessageSummaryAsync(cancellationToken);
         await _imapReceiver.MonitorFolder
-           .OnMessageArrival(OnArrivalAsync)
-           .IdleAsync(cancellationToken);
+            .SetIgnoreExistingMailOnConnect()
+            .OnMessageArrival(OnArrivalAsync)
+            .IdleAsync(cancellationToken);
 
         async Task OnArrivalAsync(IMessageSummary messageSummary)
         {
             try
             {
-                _logger.LogInformation($"{_imapReceiver} message #{messageSummary.UniqueId} arrived.");
-                //var mimeMessage = await _imapReceiver.ReadMail.GetMimeMessageAsync(messageSummary.UniqueId);
-                //var mimeMessage = await messageSummary.GetMimeMessageAsync();
+                if (messageSummary.UniqueId > newestEmail?.UniqueId)
+                {
+                    var mimeMessage = await messageSummary.GetMimeMessageAsync();
+                    //var mimeMessage = await _imapReceiver.ReadMail.GetMimeMessageAsync(messageSummary.UniqueId);
+                    _logger.LogInformation($"{_imapReceiver} message #{messageSummary.UniqueId} arrived, {mimeMessage.MessageId}.");
+                }
+                else
+                    _logger.LogInformation($"{_imapReceiver} message #{messageSummary.UniqueId} arrived.");
             }
             catch (Exception ex)
             {
@@ -52,6 +61,17 @@ async Task OnArrivalAsync(IMessageSummary messageSummary)
         }
     }
 
+    public async Task<IMessageSummary?> GetNewestMessageSummaryAsync(CancellationToken cancellationToken = default)
+    {
+        using var mailFolderClient = _imapReceiver.MailFolderClient;
+        var mailFolder = await mailFolderClient.ConnectAsync(false, cancellationToken).ConfigureAwait(false);
+        var index = mailFolder.Count - 1;
+        var filter = MessageSummaryItems.UniqueId;
+        var messageSummaries = await mailFolder.FetchAsync(index, index, filter, cancellationToken).ConfigureAwait(false);
+        await mailFolder.CloseAsync(false, CancellationToken.None).ConfigureAwait(false);
+        return messageSummaries.FirstOrDefault();
+    }
+
     private async Task GetMessageSummaryRepliesAsync(CancellationToken cancellationToken = default)
     {
         var stopwatch = Stopwatch.StartNew();

source/MailKitSimplified.Receiver/Extensions/EmailReceiverExtensions.cs

@@ -1,4 +1,5 @@
-using MailKit.Search;
+using MailKit;
+using MailKit.Search;
 using System;
 using System.Linq;
 using System.Threading;
@@ -13,16 +14,15 @@ public static class EmailReceiverExtensions
         public static string ToEnumeratedString<T>(this IEnumerable<T> data, string div = ", ") =>
             data is null ? "" : string.Join(div, data.Select(o => o?.ToString() ?? ""));
 
-        public static IList<T> TryAddUniqueRange<T>(this IList<T> list, IEnumerable<T> items)
-        {
+        public static IList<T> TryAddUniqueRange<T>(this IList<T> list, IEnumerable<T> items) where T : IMessageSummary        {
             var result = new List<T>();
             if (list is null)
                 list = new List<T>();
             if (items != null)
             {
                 foreach (T item in items)
                 {
-                    if (item != null && !list.Contains(item))
+                    if (item != null && !list.Any(m => m.UniqueId == item.UniqueId))
                     {
                         list.Add(item);
                         result.Add(item);

source/MailKitSimplified.Receiver/Services/MailFolderMonitor.cs

@@ -30,6 +30,7 @@ public sealed class MailFolderMonitor : IMailFolderMonitor
         private CancellationTokenSource _arrival = new CancellationTokenSource();
         private CancellationTokenSource _cancel;
         private IImapClient _imapClient;
+        private IImapClient _fetchClient;
         private IMailFolder _mailFolder;
         private IMailFolder _fetchFolder;
         private bool _canIdle;
@@ -151,6 +152,7 @@ private async Task IdleStartAsync(CancellationToken cancellationToken = default)
                 {
                     _imapClient = await _imapReceiver.ConnectAuthenticatedImapClientAsync(cancellationToken).ConfigureAwait(false);
                     _canIdle = _imapClient.Capabilities.HasFlag(ImapCapabilities.Idle);
+                    _fetchClient = await _fetchReceiver.ConnectAuthenticatedImapClientAsync(cancellationToken).ConfigureAwait(false);
                     _fetchFolder = await _fetchReceiver.ConnectMailFolderAsync(cancellationToken).ConfigureAwait(false);
                     _ = await _fetchFolder.OpenAsync(FolderAccess.ReadOnly, cancellationToken).ConfigureAwait(false);
                     _mailFolder = await _imapReceiver.ConnectMailFolderAsync(cancellationToken).ConfigureAwait(false);
@@ -295,9 +297,13 @@ private async ValueTask WaitForNewMessagesAsync(CancellationToken cancellationTo
         private async ValueTask<int> ProcessMessagesArrivedAsync(bool firstConnection = false, CancellationToken cancellationToken = default)
         {
             int startIndex = _messageCache.Count;
-            _logger.LogTrace($"{_fetchReceiver} ({_fetchFolder.Count}) Fetching new message arrivals, starting from {startIndex}.");
+            await _fetchClient.NoOpAsync(cancellationToken).ConfigureAwait(false);
+            _logger.LogTrace($"{_fetchReceiver} ({_fetchFolder.Count}) fetching new message arrivals, starting from {startIndex}.");
             if (startIndex > _fetchFolder.Count)
+            {
+                _logger.LogTrace($"{_fetchReceiver} start index {startIndex} is higher than fetched folder count of {_fetchFolder.Count}, monitored count is {_mailFolder.Count}.");
                 startIndex = _fetchFolder.Count;
+            }
             var filter = _folderMonitorOptions.MessageSummaryItems | MessageSummaryItems.UniqueId;
             var fetched = await _fetchFolder.FetchAsync(startIndex, -1, filter, cancellationToken).ConfigureAwait(false);
             if (_arrival.IsCancellationRequested)