analysis.cs

static void Analyze(string dir)
{
    var spearators = new char[] { ' ', '\t', ',', '!', '\r', '(', ')', '?', '-', '"', '\n', '/' };
    var trim = new char[] { '.', };

    var blockingCollection = new BlockingCollection<string>(2048);
    var tasks = new List<Task>();
    var dics = new ConcurrentQueue<Dictionary<string, HashSet<string>>>();
    for (int i = 0; i < 16; i++)
    {
        var task = Task.Run(() =>
        {
            while (blockingCollection.IsCompleted == false)
            {
                using var stream = File.OpenRead(blockingCollection.Take());

                var parser = new MimeParser(stream, MimeFormat.Entity);
                while (parser.IsEndOfStream == false)
                {
                    var entity = parser.ParseMessage();

                    var dic = new Dictionary<string, HashSet<string>>
                    {
                        ["Id"] = new HashSet<string> { entity.MessageId.ToLower() },
                        ["Date"] = new HashSet<string> { entity.Date.ToString("r") },
                        ["From"] = entity.From.Select(x => x.ToString().ToLower()).ToHashSet(),
                        ["To"] = entity.To.Select(x => x.ToString().ToLower()).ToHashSet(),
                        ["Body"] = entity.GetTextBody(TextFormat.Plain)
                            .Split(spearators, StringSplitOptions.RemoveEmptyEntries)
                            .Select(x => x.Trim(trim).ToLower())
                            .Where(x =>
                            {
                                if (x.Length > 3)
                                    return true;
                                if (x.Length == 0)
                                    return false;
                                return char.IsDigit(x[0]);
                            })
                            .ToHashSet()
                    };

                    dics.Enqueue(dic);
                }
            }
        });
        tasks.Add(task);
    }

    var so = Stopwatch.StartNew();

    tasks.Add(Task.Run(() =>
    {
        foreach (var file in Directory.EnumerateFiles(dir, "*", SearchOption.AllDirectories))
        {
            blockingCollection.Add(file);
        }
        blockingCollection.CompleteAdding();
    }));

    var final = Task.WhenAll(tasks.ToArray());

    // do stuff with it.

}