public EnvelopeCollection LastDownloadedEnvelopes { get; }

Public ReadOnly Property LastDownloadedEnvelopes As EnvelopeCollection
	Get

using System;
using MailBee;
using MailBee.ImapMail;

class Sample
{
    static int  traffic;
    static bool downloadingEnvelopes;

    // We use Imap.DataReceived event to simulate connection drop during
    // getting message data from the server. We do this through closing
    // the connection after 50000 bytes of message data has been received from the
    // server. This may occur multiple times (for instance, if there is 1MB of mail
    // in the inbox, the connection will be dropped about 20 times).
    // If, however, there is a message larger than 50KB in the inbox, the download process
    // will stop because it would otherwise end up in an endless loop (because this code
    // always disconnects on getting 50-th KB of the data and it would never have received
    // such message completely).
    static void imp_DataReceived(object sender, DataTransferEventArgs e)
    {
        if (downloadingEnvelopes)
        {
            traffic += e.Data.Length;

            // Increase 50000 to a larger value if you wish to test this code with
            // a mailbox containing large messages (larger than 50KB).
            if (traffic > 50000)
            {
                ((Imap)sender).Log.WriteLine("SIMULATE CONNECTION DROP");
                ((Imap)sender).GetSocket().Close();
            }
        }
    }

    static void Main(string[] args)
    {
        Imap imp = new Imap();

        // Enable logging IMAP4 session into a file. Useful for troubleshooting.
        // Also, this log can be used to track the history of disconnections and
        // reconnections during downloading messages.
        imp.Log.Filename = @"C:\Temp\log.txt";
        imp.Log.Enabled = true;
        imp.Log.Clear();

        // Attach to a DataReceived event which will be used for simulating
        // connection failures.
        imp.DataReceived += new DataTransferEventHandler(imp_DataReceived);

        // Will set it to true once either everything has been downloaded
        // or a permanent error has occurred.
        bool finished = false;

        // Remember UID of the last message which had already been downloaded.
        // After reconnecting, we'll download envelopes with UIDs larger than
        // lastUid. For the first time, set it to 0 (which is less than UID of
        // any message because minimum value of UID is 1).
        long lastUid = 0;

        // We'll collect downloaded messages in this collection.
        EnvelopeCollection envs = new EnvelopeCollection();

        // Because we catch exceptions in this code but still want to know
        // which error has occurred in the case of permanent failure, we remember
        // the reason of it.
        MailBeeException permanentException = null;

        // Enable cache of envelopes downloaded during execution of the last method.
        imp.EnableLastDownloaded = true;

        do
        {
            // Prevent connection drop simulation when not downloading messages.
            downloadingEnvelopes = false;

            // Connect or reconnect to the server if required (and login/select inbox).
            if (!imp.IsConnected)
            {
                imp.Connect("mail.domain.com");
            }
            if (!imp.IsLoggedIn)
            {
                imp.Login("jdoe", "secret");
            }
            if (!imp.IsFolderSelected)
            {
                imp.SelectFolder("INBOX");
            }

            traffic = 0;

            try
            {
                // Enable connection drop simulation.
                downloadingEnvelopes = true;

                // Download the remaining messages.
                imp.DownloadEnvelopes((lastUid + 1).ToString() + ":*", true, EnvelopeParts.MessagePreview, -1);

                // Disable connection drop simulation.
                downloadingEnvelopes = false;

                // All's done.
                envs.Add(imp.LastDownloadedEnvelopes);
                finished = true;
            }
            catch (MailBeeException e)
            {
                downloadingEnvelopes = false;

                if (imp.LastDownloadedEnvelopes == null ||
                    imp.LastDownloadedEnvelopes.Count == 0)
                {
                    // Haven't got any messages. Assume this is permanent error
                    // (otherwise, we could get endless loop).
                    finished = true;
                    permanentException = e;
                }
                else
                {
                    // Error has occurred but some envelopes have still been
                    // downloaded. We'll proceed with getting the rest of messages.
                    envs.Add(imp.LastDownloadedEnvelopes);

                    // Get last UID from the value of UID of the last downloaded message.
                    lastUid = imp.LastDownloadedEnvelopes[imp.LastDownloadedEnvelopes.Count - 1].Uid;
                }
            }
        } while (!finished);

        // Clear and disable the cache of the last downloaded envelopes.
        imp.EnableLastDownloaded = false;

        if (imp.IsConnected)
        {
            // Attempt to disconnect (we need to catch MailBeeSocketObjectDisposedException
            // here because we simulated connection drop bypassing MailBee (using Socket.Close()
            // method) and Imap.IsConnected could remain true). In real world apps, this
            // is not required and Imap.IsConnected always reflects the actual state of
            // the connection.
            try
            {
                imp.Disconnect();
            }
            catch (MailBeeSocketObjectDisposedException) {}
        }

        // Display UIDs of the downloaded messages.
        foreach (Envelope env in envs)
        {
            Console.Write(env.Uid + " ");
        }
    }
}

Imports System
Imports MailBee
Imports MailBee.ImapMail

Class Sample
    Shared traffic As Integer
    Shared downloadingEnvelopes As Boolean

    ' We use Imap.DataReceived event to simulate connection drop during
    ' getting message data from the server. We do this through closing
    ' the connection after 50000 bytes of message data has been received from the
    ' server. This may occur multiple times (for instance, if there is 1MB of mail
    ' in the inbox, the connection will be dropped about 20 times).
    ' If, however, there is a message larger than 50KB in the inbox, the download process
    ' will stop because it would otherwise end up in an endless loop (because this code
    ' always disconnects on getting 50-th KB of the data and it would never have received
    ' such message completely).
    Shared Sub imp_DataReceived(ByVal sender As Object, ByVal e As DataTransferEventArgs)
        If downloadingEnvelopes Then
            traffic += e.Data.Length

            ' Increase 50000 to a larger value if you wish to test this code with
            ' a mailbox containing large messages (larger than 50KB).
            If traffic > 50000 Then
                CType(sender, Imap).Log.WriteLine("SIMULATE CONNECTION DROP")
                CType(sender, Imap).GetSocket().Close()
            End If
        End If
    End Sub

    Shared Sub Main(ByVal args() As String)
        Dim imp As Imap = New Imap

        ' Enable logging IMAP4 session into a file. Useful for troubleshooting.
        ' Also, this log can be used to track the history of disconnections and
        ' reconnections during downloading messages.
        imp.Log.Filename = "C:\Temp\log.txt"
        imp.Log.Enabled = True
        imp.Log.Clear()

        ' Attach to a DataReceived event which will be used for simulating
        ' connection failures.
        AddHandler imp.DataReceived, AddressOf imp_DataReceived

        ' Will set it to true once either everything has been downloaded
        ' or a permanent error has occurred.
        Dim finished As Boolean = False

        ' Remember UID of the last message which had already been downloaded.
        ' After reconnecting, we'll download envelopes with UIDs larger than
        ' lastUid. For the first time, set it to 0 (which is less than UID of
        ' any message because minimum value of UID is 1).
        Dim lastUid As Long = 0

        ' We'll collect downloaded messages in this collection.
        Dim envs As EnvelopeCollection = New EnvelopeCollection

        ' Because we catch exceptions in this code but still want to know
        ' which error has occurred in the case of permanent failure, we remember
        ' the reason of it.
        Dim permanentException As MailBeeException = Nothing

        ' Enable cache of envelopes downloaded during execution of the last method.
        imp.EnableLastDownloaded = True

        Do
            ' Prevent connection drop simulation when not downloading messages.
            downloadingEnvelopes = False

            ' Connect or reconnect to the server if required (and login/select inbox).
            If Not imp.IsConnected Then
                imp.Connect("mail.domain.com")
            End If
            If Not imp.IsLoggedIn Then
                imp.Login("jdoe", "secret")
            End If
            If Not imp.IsFolderSelected Then
                imp.SelectFolder("INBOX")
            End If

            traffic = 0

            Try
                ' Enable connection drop simulation.
                downloadingEnvelopes = True

                ' Download the remaining messages.
                imp.DownloadEnvelopes((lastUid + 1).ToString() & ":*", True, EnvelopeParts.MessagePreview, -1)

                ' Disable connection drop simulation.
                downloadingEnvelopes = False

                ' All's done.
                envs.Add(imp.LastDownloadedEnvelopes)
                finished = True
            Catch e As MailBeeException
                downloadingEnvelopes = False

                If imp.LastDownloadedEnvelopes Is Nothing Or imp.LastDownloadedEnvelopes.Count = 0 Then
                    ' Haven't got any messages. Assume this is permanent error
                    ' (otherwise, we could get endless loop).
                    finished = True
                    permanentException = e
                Else
                    ' Error has occurred but some envelopes have still been
                    ' downloaded. We'll proceed with getting the rest of messages.
                    envs.Add(imp.LastDownloadedEnvelopes)

                    ' Get last UID from the value of UID of the last downloaded message.
                    lastUid = imp.LastDownloadedEnvelopes(imp.LastDownloadedEnvelopes.Count - 1).Uid
                End If
            End Try
        Loop While Not finished

        ' Clear and disable the cache of the last downloaded envelopes.
        imp.EnableLastDownloaded = False

        If imp.IsConnected Then
            ' Attempt to disconnect (we need to catch MailBeeSocketObjectDisposedException
            ' here because we simulated connection drop bypassing MailBee (using Socket.Close()
            ' method) and Imap.IsConnected could remain true). In real world apps, this
            ' is not required and Imap.IsConnected always reflects the actual state of
            ' the connection.
            Try
                imp.Disconnect()
            Catch e As MailBeeSocketObjectDisposedException
            End Try
        End If

        ' Display UIDs of the downloaded messages.
        Dim env As Envelope
        For Each env In envs
            Console.Write(env.Uid & " ")
        Next
    End Sub
End Class