public class EmailAddressValidator : IComponent, 
	IDisposable

Public Class EmailAddressValidator
	Implements IComponent, IDisposable

using System;
using System.IO;
using System.Data;
using MailBee;
using MailBee.AddressCheck;

class Program
{
    const string EmailColumn = "email";
    const string FailureCountColumn = "failures";
    private static StreamWriter sw = null;

    // Builds the data table from the file contents.
    // For brevity, we don't check if the data has correct format.
    private static DataTable GetDataTable(string[] lines)
    {
        DataTable workTable = new DataTable();
        workTable.Columns.Add(EmailColumn, typeof(string));
        workTable.Columns.Add(FailureCountColumn, typeof(int));

        foreach (string line in lines)
        {
            string[] parts = line.Split(',');
            DataRow row = workTable.NewRow();
            row[EmailColumn] = parts[0];
            row[FailureCountColumn] = int.Parse(parts[1]);
            workTable.Rows.Add(row);
        }

        return workTable;
    }

    // This method will be executed for each e-mail address in the bulk,
    // whenever it gets verified. Those addresses for which we set VerifyIt
    // to 'false' will be skipped from further verification and Verified
    // event won't occur for them.
    private static void valid_Verifying(object sender, VerifyingEventArgs e)
    {
        try
        {
            Console.WriteLine(string.Format("{0} is being checked against blacklist.", e.Email));

            if (e.Email.EndsWith("@blacklisted.com"))
            {
                // Exclude it from address checking by other methods, and forget it.
                e.VerifyIt = false;
                Console.WriteLine(string.Format("{0} removed due to blacklist hit.", e.Email));
            }

            if (e.VerifyIt)
            {
                Console.WriteLine(string.Format("{0} survived blacklist check.", e.Email));
            }
            else
            {
                Console.WriteLine(string.Format("Discarded: {0}", e.Email));
            }
        }
        catch (Exception ex)
        {
            // At least for debug purposes, it makes sense to catch all exceptions in
            // event handlers as uncaught exceptions here don't cause the app to crash.
            // Without this try/catch, it could be quite hard to understand what went wrong
            // as you'd see no indication of a problem, the event handler would silently
            // die in the middle but the app itself would continue.
            Console.WriteLine(ex.ToString());
        }

        Console.WriteLine();
    }

    // All those e-mail addresses which survived Verifying event handler then get validated,
    // and the validation results (which can be both successful or negative) will be delivered
    // to the application through Verified event handler.
    private static void valid_Verified(object sender, VerifiedEventArgs e)
    {
        try
        {
            // Keep the address on the list?
            bool keepIt;

            Console.WriteLine(string.Format("{0}={1}", e.Email, e.Result.ToString()));
            if (e.Reason != null)
            {
                Console.WriteLine("Reason: " + e.Reason.Message);
            }
            int failureCount = (int)e.Row[FailureCountColumn];
            switch (e.Result)
            {
                case AddressValidationLevel.OK:
                    // Address is fine, reset the failure counter if needed.
                    if (failureCount != 0)
                    {
                        failureCount = 0;
                    }
                    keepIt = true;
                    break;
                case AddressValidationLevel.RegexCheck:
                    // Bad syntax, won't keep this address in the list.
                    keepIt = false;
                    break;
                default:
                    failureCount++;
                    if (failureCount > 3)
                    {
                        // Too many failed attempts. Forget this address.
                        keepIt = false;
                    }
                    else
                    {
                        // Give the address another chance.
                        keepIt = true;
                    }
                    break;
            }

            if (keepIt)
            {
                sw.WriteLine(string.Format("{0},{1}", e.Email, failureCount.ToString()));
                Console.WriteLine(string.Format("Written to the file: {0},{1}",
                    e.Email, failureCount.ToString()));
            }
            else
            {
                Console.WriteLine(string.Format("Discarded: {0}", e.Email));
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        Console.WriteLine();
    }

    static void Main(string[] args)
    {
        EmailAddressValidator valid = new EmailAddressValidator("MN110-0123456789ABCDEF-0123");

        // To perform DNS MX lookup queries, we need some DNS servers for that.
        valid.DnsServers.Autodetect();

        // Logging into a file is not required for the component to work
        // but helpful for debugging and understanding things under the hood.
        valid.Log.Enabled = true;
        valid.Log.Filename = @"C:\Temp\log.txt";
        valid.Log.Clear();

        // Subscribe to events.
        valid.Verifying += new VerifyingEventHandler(valid_Verifying);
        valid.Verified += new VerifiedEventHandler(valid_Verified);

        string inputFile = @"C:\Temp\input.txt";
        string outputFile = @"C:\Temp\output.txt";

        // Create a file with some e-mail addresses to check if it's not already there.
        if (!File.Exists(inputFile))
        {
            // Number is a count of failed attempts to check an address. If it exceeds 3, we'll
            // remove the address from the list. Addresses with invalid syntax will be removed
            // immediately.
            File.WriteAllText(inputFile,
@"john.doe@domain.com,0
user@blacklisted.com,0
alice@company.com,0
somebody@non-exisent.domain,0
bob@incorrect-syntax,0
sarah@example.com,0");
        }

        string[] lines = File.ReadAllLines(inputFile);

        if (lines.Length == 0)
        {
            Console.WriteLine("No addresses left in the list! Delete input.txt and try again.");
        }

        using (sw = new StreamWriter(outputFile))
        {
            // Run the verification in single-threaded mode (for clarity of console output).
            valid.Verify(GetDataTable(lines), EmailColumn);
        }

        // Once the verification finished, replace the input file with the recently generated.
        // This way, we'll refine our list each time the app is run. After several runs, only
        // good addresses will remain.
        File.Delete(inputFile);
        File.Move(outputFile, inputFile);
    }
}

Imports System.IO
Imports System.Data
Imports MailBee
Imports MailBee.AddressCheck

Class Program
    Const EmailColumn As String = "email"
    Const FailureCountColumn As String = "failures"
    Private Shared sw As StreamWriter = Nothing

    ' Builds the data table from the file contents.
    ' For brevity, we don't check if the data has correct format.
    Private Shared Function GetDataTable(ByVal lines As String()) As DataTable
        Dim workTable As New DataTable()
        workTable.Columns.Add(EmailColumn, GetType(String))
        workTable.Columns.Add(FailureCountColumn, GetType(Integer))

        For Each line As String In lines
            Dim parts As String() = line.Split(","c)
            Dim row As DataRow = workTable.NewRow()
            row(EmailColumn) = parts(0)
            row(FailureCountColumn) = Integer.Parse(parts(1))
            workTable.Rows.Add(row)
        Next

        Return workTable
    End Function

    ' This method will be executed for each e-mail address in the bulk,
    ' whenever it gets verified. Those addresses for which we set VerifyIt
    ' to 'false' will be skipped from further verification and Verified
    ' event won't occur for them.
    Private Shared Sub valid_Verifying(ByVal sender As Object, ByVal e As VerifyingEventArgs)
        Try
            Console.WriteLine(String.Format("{0} is being checked against blacklist.", e.Email))

            If e.Email.EndsWith("@blacklisted.com") Then
                ' Exclude it from address checking by other methods, and forget it.
                e.VerifyIt = False
                Console.WriteLine(String.Format("{0} removed due to blacklist hit.", e.Email))
            End If

            If e.VerifyIt Then
                Console.WriteLine(String.Format("{0} survived blacklist check.", e.Email))
            Else
                Console.WriteLine(String.Format("Discarded: {0}", e.Email))
            End If
        Catch ex As Exception
            ' At least for debug purposes, it makes sense to catch all exceptions in
            ' event handlers as uncaught exceptions here don't cause the app to crash.
            ' Without this try/catch, it could be quite hard to understand what went wrong
            ' as you'd see no indication of a problem, the event handler would silently
            ' die in the middle but the app itself would continue.
            Console.WriteLine(ex.ToString())
        End Try

        Console.WriteLine()
    End Sub

    ' All those e-mail addresses which survived Verifying event handler then get validated,
    ' and the validation results (which can be both successful or negative) will be delivered
    ' to the application through Verified event handler.
    Private Shared Sub valid_Verified(ByVal sender As Object, ByVal e As VerifiedEventArgs)
        Try
            ' Keep the address on the list?
            Dim keepIt As Boolean

            Console.WriteLine(String.Format("{0}={1}", e.Email, e.Result.ToString()))
            If Not (e.Reason Is Nothing) Then
                Console.WriteLine("Reason: " & e.Reason.Message)
            End If
            Dim failureCount As Integer = CInt(e.Row(FailureCountColumn))
            Select Case e.Result
                Case AddressValidationLevel.OK
                    ' Address is fine, reset the failure counter if needed.
                    If failureCount <> 0 Then
                        failureCount = 0
                    End If
                    keepIt = True
                    Exit Select
                Case AddressValidationLevel.RegexCheck
                    ' Bad syntax, won't keep this address in the list.
                    keepIt = False
                    Exit Select
                Case Else
                    failureCount += 1
                    If failureCount > 3 Then
                        ' Too many failed attempts. Forget this address.
                        keepIt = False
                    Else
                        ' Give the address another chance.
                        keepIt = True
                    End If
                    Exit Select
            End Select

            If keepIt Then
                sw.WriteLine(String.Format("{0},{1}", e.Email, failureCount.ToString()))
                Console.WriteLine(String.Format("Written to the file: {0},{1}", _
                 e.Email, failureCount.ToString()))
            Else
                Console.WriteLine(String.Format("Discarded: {0}", e.Email))
            End If
        Catch ex As Exception
            Console.WriteLine(ex.ToString())
        End Try

        Console.WriteLine()
    End Sub

    Shared Sub Main(ByVal args As String())
        Dim valid As New EmailAddressValidator("MN110-0123456789ABCDEF-0123")

        ' To perform DNS MX lookup queries, we need some DNS servers for that.
        valid.DnsServers.Autodetect()

        ' Logging into a file is not required for the component to work
        ' but helpful for debugging and understanding things under the hood.
        valid.Log.Enabled = True
        valid.Log.Filename = "C:\Temp\log.txt"
        valid.Log.Clear()

        ' Subscribe to events.
        AddHandler valid.Verifying, AddressOf valid_Verifying
        AddHandler valid.Verified, AddressOf valid_Verified

        Dim inputFile As String = "C:\Temp\input.txt"
        Dim outputFile As String = "C:\Temp\output.txt"

        ' Create a file with some e-mail addresses to check if it's not already there.
        If Not File.Exists(inputFile) Then
            ' Number is a count of failed attempts to check an address. If it exceeds 3, we'll
            ' remove the address from the list. Addresses with invalid syntax will be removed
            ' immediately.
            File.WriteAllText(inputFile, "john.doe@domain.com,0" & vbCrLf & _
             "user@blacklisted.com,0" & vbCrLf & "alice@company.com,0" & vbCrLf & _
             "somebody@non-exisent.domain,0" & vbCrLf & "bob@incorrect-syntax,0" & vbCrLf _
             & "sarah@example.com,0")
        End If

        Dim lines As String() = File.ReadAllLines(inputFile)

        If lines.Length = 0 Then
            Console.WriteLine("No addresses left in the list! Delete input.txt and try again.")
        End If

        sw = New StreamWriter(outputFile)

        Try
            ' Run the verification in single-threaded mode (for clarity of console output).
            valid.Verify(GetDataTable(lines), EmailColumn)
        Finally
            sw.Close()
        End Try

        ' Once the verification finished, replace the input file with the recently generated.
        ' This way, we'll refine our list each time the app is run. After several runs, only
        ' good addresses will remain.
        File.Delete(inputFile)
        File.Move(outputFile, inputFile)
    End Sub
End Class