var client = new NntpClient(new NntpConnection());
await client.ConnectAsync(hostname, port, useSsl);

client.Authenticate(username, password)

NntpArticleResponse response = client.Article(messageId);
if (response.Success) {
    foreach (string line in response.Article.Body) {
        ...
    }
}

string messageId = $"{Guid.NewGuid()}@example.net";

NntpArticle newArticle = new NntpArticleBuilder()
    .SetMessageId(messageId)
    .SetFrom("Randomposter <[email protected]>")
    .SetSubject("Random test post #1")
    .AddGroups("alt.test.clienttest", "alt.test")
    .AddLine("This is a message with id " + messageId)
    .AddLine("with multiple lines")
    .Build();

client.Post(newArticle);

NzbDocument nzbDocument = NzbParser.Parse(File.ReadAllText(nzbPath));

foreach (NzbFile file in nzbDocument.Files)
{
    foreach (NzbSegment segment in file.Segments)
    {
        // retrieve article from Usenet server
        NntpArticleResponse response = client.Article(segment.MessageId);

        // decode the yEnc-encoded article
        using (YencStream yencStream = YencStreamDecoder.Decode(response.Article.Body))
        {
            YencHeader header = yencStream.Header;

            if (!File.Exists(header.FileName))
            {
                // create file and pre-allocate disk space for it
                using (FileStream stream = File.Create(header.FileName))
                {
                    stream.SetLength(header.FileSize);
                }
            }
            using (FileStream stream = File.Open(
                header.FileName, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite))
            {
                // copy incoming parts to file
                stream.Position = header.PartOffset;
                yencStream.CopyTo(stream);
            }
        }
    }
}

IFileProvider fileProvider = new PhysicalFileProvider(Path.GetFullPath("testdata"));

NzbBuilder builder = new NzbBuilder()
    .AddGroups("alt.test.clienttest")
    .SetMessageBase("random.local")
    .SetPartSize(50_000)
    .SetPoster("random poster <[email protected]>")
    .AddMetaData("title", "Testing upload Pictures.rar");

foreach (string fileName in fileNames)
{
    builder.AddFile(fileProvider.GetFileInfo(fileName));
}

NzbDocument nzbDocument = builder.Build();

using (FileStream file = File.Open("Pictures.nzb"))
using (var writer = new StreamWriter(file, UsenetEncoding.Default))
{
    await writer.WriteNzbDocumentAsync(nzbDocument);
}

foreach (NzbFile file in nzbDocument.Files)
{
    // open file stream
    IFileInfo fileInfo = fileProvider.GetFileInfo(file.FileName);
    using (Stream stream = fileInfo.CreateReadStream())
    {
        foreach (NzbSegment segment in file.Segments)
        {
            stream.Position = segment.Offset;

            // encode in yEnc format
            IEnumerable<string> encodedBody = YencEncoder.Encode(new YencHeader(
                file.FileName, file.Size, 128, segment.Number, file.Segments.Count,
                segment.Size, segment.Offset), stream);

            // create article
            NntpArticle article = new NntpArticleBuilder()
                .AddGroups(file.Groups)
                .SetMessageId(segment.MessageId)
                .SetFrom(file.Poster)
                .SetSubject(segment.MessageId)
                .SetBody(encodedBody)
                .Build();

            // post article
            client.Post(article);
        }
    }
}

client.Quit();