To authenticate to an POP3 server, you can follow the steps below

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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   C#

   VB.NET

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

   Imports System.Text
   Imports ComponentPro.Net.Mail
   

2. Create a new instance of the Pop3 class.
3. Now you can connect to the POP3 server with Connect methods. The code looks similar to the following:
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   C#

   VB.NET

   // Create a new instance of the Pop3 class.
   Pop3 client = new Pop3();
   
   // Connect to the server.
   client.Connect("myserver");
   
   // Or you can specify the POP3 port with 
   // client.Connect("myserver", 110);
   

   ' Create a new instance of the Pop3 class. 
   Dim client As New Pop3()
   
   ' Connect to the server.
   client.Connect("myserver")
   
   ' Or you can specify the POP3 port with 
   ' client.Connect("myserver", 110);
   

4. Use your user name and password to login with one of Authenticate methods. The code looks similar to the following:
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   C#

   VB.NET

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

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

5. Do your work like listing messages, downloading mail messages, etc. The code looks similar to the following:
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   C#

   VB.NET

   StringBuilder sb = new StringBuilder();
   
   Pop3MessageCollection list = client.ListMessages(Pop3EnvelopeParts.Size | Pop3EnvelopeParts.UniqueId);
   for (int i = 0; i < list.Count; i++)
   {
       sb.AppendFormat("{0} - {1}\r\n", i + 1, list[i].UniqueId);
   }
   
   Console.WriteLine(sb.ToString());
   

   Dim sb As New StringBuilder()
   
   Dim list As Pop3MessageCollection = client.ListMessages(Pop3EnvelopeParts.Size Or Pop3EnvelopeParts.UniqueId)
   For i As Integer = 0 To list.Count - 1
       sb.AppendFormat("{0} - {1}" & vbCrLf, i + 1, list(i).UniqueId)
   Next i
   
   Console.WriteLine(sb.ToString())
   

6. After completing your work, call the Disconnect method to close the POP3 session.

Final example code

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

...

// Create a new instance of the Pop3 class.
Pop3 client = new Pop3();

// Connect to the server.
client.Connect("myserver");

// Or you can specify the POP3 port with 
// client.Connect("myserver", 110); 
 
// Login to the server.
client.Authenticate("user", "password");

StringBuilder sb = new StringBuilder();

Pop3MessageCollection list = client.ListMessages(Pop3EnvelopeParts.Size | Pop3EnvelopeParts.UniqueId);
for (int i = 0; i < list.Count; i++)
{
    sb.AppendFormat("{0} - {1}\r\n", i + 1, list[i].UniqueId);
}

Console.WriteLine(sb.ToString());

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

Imports System.Text
Imports ComponentPro.Net.Mail

...

' Create a new instance of the Pop3 class. 
Dim client As New Pop3()

' Connect to the server.
client.Connect("myserver")

' Or you can specify the POP3 port with 
' client.Connect("myserver", 110); 
 
' Login to the server.
client.Authenticate("user", "password")

Dim sb As New StringBuilder()

Dim list As Pop3MessageCollection = client.ListMessages(Pop3EnvelopeParts.Size Or Pop3EnvelopeParts.UniqueId)
For i As Integer = 0 To list.Count - 1
    sb.AppendFormat("{0} - {1}" & vbCrLf, i + 1, list(i).UniqueId)
Next i

Console.WriteLine(sb.ToString())

' Close the connection.
client.Disconnect()