Visual Basic

var sender = new EmailSender();

sender.SendEmailCompleted += (o, eventArgs) 
  => Console.WriteLine(eventArgs.RetryCount);

sender.SendEmailAsync(new MailMessage(), 5);

Dim sender As var = New EmailSender
sender.SendEmailCompleted = (sender.SendEmailCompleted + o)
,eventArgs
Unknown=GreaterConsole.WriteLine(eventArgs.RetryCount)
sender.SendEmailAsync(New MailMessage, 5)

Imports System.ComponentModel
Imports System.Net.Mail

Public Class SendEngine

    Private _currentRetryCount As Integer
    Private _maxRetryCount As Integer
    Private _mailMessage As MailMessage
    Private _isAlreadyRun As Boolean
    Public Event SendEmailCompleted As SendEmailCompletedEventHandler

    Public Sub SendEmailAsync(ByVal smtpClient As SmtpClient, ByVal message As MailMessage, ByVal retryCount As Integer)

        If _isAlreadyRun Then
            Throw New InvalidOperationException("sendEngine doesn't support multiple concurrent invocations.")
        End If

        _isAlreadyRun = True
        _maxRetryCount = retryCount
        _mailMessage = message

        AddHandler smtpClient.SendCompleted, AddressOf SmtpClientSendCompleted

        SendMessage(smtpClient)

    End Sub
    Private Sub SendMessage(ByVal smtpClient As SmtpClient)

        Try
            smtpClient.SendAsync(_mailMessage, Guid.NewGuid)

        Catch exception As Exception

            EndProcessing(smtpClient)

        End Try

    End Sub
    Private Sub EndProcessing(ByVal smtpClient As SmtpClient)

        If (_mailMessage IsNot Nothing) Then
            _mailMessage.Dispose()
        End If

        If (smtpClient IsNot Nothing) Then

            RemoveHandler smtpClient.SendCompleted, AddressOf SmtpClientSendCompleted
            smtpClient.Dispose()

        End If

        OnSendCompleted(New SendEmailCompletedEventArgs(Nothing, False, Nothing, _currentRetryCount))

        _isAlreadyRun = False
        _currentRetryCount = 0

    End Sub
    Private Sub SmtpClientSendCompleted(ByVal sender As Object, ByVal e As AsyncCompletedEventArgs)

        Dim smtpClient = CType(sender, SmtpClient)
        If ((e.Error Is Nothing) OrElse (_currentRetryCount >= _maxRetryCount)) Then

            EndProcessing(smtpClient)

        Else

            _currentRetryCount = (_currentRetryCount + 1)
            SendMessage(smtpClient)

        End If

    End Sub
    Protected Overridable Sub OnSendCompleted(ByVal args As SendEmailCompletedEventArgs)

        RaiseEvent SendEmailCompleted(Me, args)

    End Sub

End Class

Public Delegate Sub SendEmailCompletedEventHandler(ByVal sender As Object, ByVal e As SendEmailCompletedEventArgs)

Public Class SendEmailCompletedEventArgs
    Inherits AsyncCompletedEventArgs

    Private mRetryCount As Integer

    Public Sub New(ByVal ex As Exception, ByVal canceled As Boolean, ByVal userState As Object, ByVal retryCount As Integer)

        MyBase.New(ex, canceled, userState)
        retryCount = retryCount

    End Sub

    Public Property RetryCount As Integer
        Get
            Return mRetryCount
        End Get

        Set(value As Integer)
            value = mRetryCount
        End Set

    End Property

End Class