Progress Event

public event EventHandler<TEventArgs> Progress

Public Event Progress EventHandler(Of TEventArgs)

public:
 event EventHandler<TEventArgs>^ Progress

Show how to handle the Progress event.

using System;
using ComponentPro.Net.Mail;

...

private long _messageSize;

public void ShowProgress()
{
    // Create a new Pop3 instance. 
    Pop3 client = new Pop3();

    // Connect to the POP3 server. 
    client.Connect("myserver");

    // Authenticate. 
    client.Authenticate("test", "test");

    try 
    {
        // Register an event handler. 
        client.Progress += client_Progress;

        Pop3MessageCollection list = client.ListMessages(Pop3EnvelopeParts.Size | Pop3EnvelopeParts.MessageInboxIndex);
        // Download the first message. 
        _messageSize = list[0].Size;

        // Download the first one. 
        client.DownloadMessage(list[0].MessageInboxIndex, "c:\\temp\\my message.eml");
    }
    catch (Pop3Exception exc)
    {
        Console.WriteLine("Exception: " + exc.Message);
    }

    // Disconnect. 
    client.Disconnect();
}

void client_Progress(object sender, Pop3ProgressEventArgs e)
{
    // Show progress information. 
    if (e.State == Pop3TransferState.Downloading)
    {
        Console.Write("\rDownloaded: {0} bytes ({1}% completed)", e.BytesTransferred, e.CalculatePercentage(_messageSize));
    }
}

Imports ComponentPro.Net.Mail

...

Private _messageSize As Long 
 
Public Sub ShowProgress()
    ' Create a new Pop3 instance. 
    Dim client As New Pop3()

    ' Connect to the POP3 server. 
    client.Connect("myserver")

    ' Authenticate. 
    client.Authenticate("test", "test")

    Try 
        ' Register an event handler. 
        AddHandler client.Progress, AddressOf client_Progress

        Dim list As Pop3MessageCollection = client.ListMessages(Pop3EnvelopeParts.Size Or Pop3EnvelopeParts.MessageInboxIndex)
        ' Download the first message. 
        _messageSize = list(0).Size

        ' Download the first one. 
        client.DownloadMessage(list(0).MessageInboxIndex, "c:\temp\my message.eml")
    Catch exc As Pop3Exception
        Console.WriteLine("Exception: " & exc.Message)
    End Try 
 
    ' Disconnect. 
    client.Disconnect()
End Sub 
 
Private Sub client_Progress(ByVal sender As Object, ByVal e As Pop3ProgressEventArgs)
    ' Show progress information. 
    If e.State = Pop3TransferState.Downloading Then 
        Console.Write(vbCr & "Downloaded: {0} bytes ({1}% completed)", e.BytesTransferred, e.CalculatePercentage(_messageSize))
    End If 
End Sub

Reference