You can either retrieve a message as an instance of the MailMessage class or download it as a raw EML message to disk or write it into a data stream with DownloadMessage method.

The following steps will help you to do that:

Downloading a Raw(.EML) Message

1. Add using directives to your code to create aliases for existing namespaces and avoid having to type the fully qualified type names. The code looks similar to the following:
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   VB.NET

   using System;
   using System.Text;
   using ComponentPro.Net;
   using ComponentPro.Net.Mail;
   

   Imports System.Text
   Imports ComponentPro.Net
   Imports ComponentPro.Net.Mail
   

2. Create a new instance of the Imap class.
3. Now you can connect to the IMAP server with Connect methods. The code looks similar to the following:
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   // IMAP server information. 
   const string serverName = "myserver";
   const string user = "name@domain.com";
   const string password = "mytestpassword";
   const int port = 993;
   const SslSecurityMode securityMode = SslSecurityMode.Implicit;
   
   // Create a new instance of the Imap class.
   Imap client = new Imap();
   
   // Connect to the server.
   client.Connect(serverName, port, securityMode);
   

   ' IMAP server information. 
   Const serverName As String = "myserver" 
   Const user As String = "name@domain.com" 
   Const password As String = "mytestpassword" 
   Const port As Integer = 993
   Const securityMode As SslSecurityMode = SslSecurityMode.Implicit
   
   ' Create a new instance of the Imap class. 
   Dim client As New Imap()
   
   ' Connect to the server.
   client.Connect(serverName, port, securityMode)
   

4. Use your user name and password to login with Authenticate methods.  The code looks similar to the following:
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   VB.NET

   // Login to the server.
   client.Authenticate(user, password);
   

   ' Login to the server.
   client.Authenticate(user, password)
   

5. Now select a working mailbox, list all message and download them to local disk with DownloadMessage. The code looks similar to the following:
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   // Select 'INBOX' mailbox
   client.Select("INBOX");
   
   // Get the message list.
   Console.WriteLine("Getting message list...");
   ImapMessageCollection list = client.ListMessages(ImapEnvelopeParts.UniqueId);
   
   // Get messages. 
   for (int i = 0; i < list.Count; i++)
   {
       ImapMessage message = list[i];
   
       // Get file name. 
       string filename = GetFilename(message.UniqueId) + ".eml";
   
       // Get new message only. 
       if (!System.IO.File.Exists(filename))
       {
           Console.WriteLine("Downloading message {0}...", message.UniqueId);
           client.DownloadMessage(message.UniqueId, filename);
       }
   }
   

   ' Select 'INBOX' mailbox
   client.Select("INBOX")
   
   ' Get the message list.
   Console.WriteLine("Getting message list...")
   Dim list As ImapMessageCollection = client.ListMessages(ImapEnvelopeParts.UniqueId)
   
   ' Get messages. 
   For i As Integer = 0 To list.Count - 1
       Dim message As ImapMessage = list(i)
   
       ' Get file name. 
       Dim filename As String = GetFilename(message.UniqueId) & ".eml" 
    
       ' Get new message only. 
       If Not System.IO.File.Exists(filename) Then 
           Console.WriteLine("Downloading message {0}...", message.UniqueId)
           client.DownloadMessage(message.UniqueId, filename)
       End If 
   Next i
   

6. After completing your work, call the Disconnect method to close the IMAP session. 

Final example code

using System;
using System.Text;
using ComponentPro.Net;
using ComponentPro.Net.Mail;

...

static void Main()
{
    // IMAP server information. 
    const string serverName = "myserver";
    const string user = "name@domain.com";
    const string password = "mytestpassword";
    const int port = 993;
    const SslSecurityMode securityMode = SslSecurityMode.Implicit;

    // Create a new instance of the Imap class. 
    Imap client = new Imap();

    // Connect to the server. 
    client.Connect(serverName, port, securityMode);

    // Login to the server. 
    client.Authenticate(user, password);

    // Select 'INBOX' mailbox 
    client.Select("INBOX");

    // Get the message list. 
    Console.WriteLine("Getting message list...");
    ImapMessageCollection list = client.ListMessages(ImapEnvelopeParts.UniqueId);

    // Get messages. 
    for (int i = 0; i < list.Count; i++)
    {
        ImapMessage message = list[i];

        // Get file name. 
        string filename = GetFilename(message.UniqueId) + ".eml";

        // Get new message only. 
        if (!System.IO.File.Exists(filename))
        {
            Console.WriteLine("Downloading message {0}...", message.UniqueId);
            client.DownloadMessage(message.UniqueId, filename);
        }
    }

    // Close the connection. 
    client.Disconnect();
}

/// <summary> 
/// Returns a uniquely correct file name from the specified unique message ID. 
/// </summary> 
/// <param name="uniqueId">The unique id.</param> 
/// <returns>The corrected file name.</returns> 
private static string GetFilename(string uniqueId)
{
    // Characters allowed in the filename 
    const string allowed = " .-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    // Replace invalid charactes with its hex representation 
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < uniqueId.Length; i++)
    {
        if (allowed.IndexOf(uniqueId[i]) < 0)
            sb.AppendFormat("_{0:X2}", (int)uniqueId[i]);
        else 
            sb.Append(uniqueId[i]);
    }
    return sb.ToString();
}

Imports System.Text
Imports ComponentPro.Net
Imports ComponentPro.Net.Mail

...

Shared Sub Main()
    ' IMAP server information. 
    Const serverName As String = "myserver" 
    Const user As String = "name@domain.com" 
    Const password As String = "mytestpassword" 
    Const port As Integer = 993
    Const securityMode As SslSecurityMode = SslSecurityMode.Implicit

    ' Create a new instance of the Imap class. 
    Dim client As New Imap()

    ' Connect to the server. 
    client.Connect(serverName, port, securityMode)

    ' Login to the server. 
    client.Authenticate(user, password)

    ' Select 'INBOX' mailbox 
    client.Select("INBOX")

    ' Get the message list. 
    Console.WriteLine("Getting message list...")
    Dim list As ImapMessageCollection = client.ListMessages(ImapEnvelopeParts.UniqueId)

    ' Get messages. 
    For i As Integer = 0 To list.Count - 1
        Dim message As ImapMessage = list(i)

        ' Get file name. 
        Dim filename As String = GetFilename(message.UniqueId) & ".eml" 
 
        ' Get new message only. 
        If Not System.IO.File.Exists(filename) Then 
            Console.WriteLine("Downloading message {0}...", message.UniqueId)
            client.DownloadMessage(message.UniqueId, filename)
        End If 
    Next i

    ' Close the connection. 
    client.Disconnect()
End Sub 
 
''' <summary> 
''' Returns a uniquely correct file name from the specified unique message ID. 
''' </summary> 
''' <param name="uniqueId">The unique id.</param> 
''' <returns>The corrected file name.</returns> 
Private Shared Function GetFilename(ByVal uniqueId As String) As String 
    ' Characters allowed in the filename 
    Const allowed As String = " .-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" 
 
    ' Replace invalid charactes with its hex representation 
    Dim sb As New StringBuilder()
    For i As Integer = 0 To uniqueId.Length - 1
        If allowed.IndexOf(uniqueId.Chars(i)) < 0 Then 
            sb.AppendFormat("_{0:X2}", System.Convert.ToInt32(uniqueId.Chars(i)))
        Else 
            sb.Append(uniqueId.Chars(i))
        End If 
    Next i
    Return sb.ToString()
End Function