Public Class MailForm
    Private sc As System.Net.Mail.SmtpClient

    Private Sub MailForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        sc = New System.Net.Mail.SmtpClient
        AddHandler sc.SendCompleted, AddressOf SendCompletedCallback
    End Sub

    Private Sub SendCompletedCallback(ByVal sender As Object, _
                                     ByVal e As AsyncCompletedEventArgs)
        ' [...]
    End Sub

    Private Sub SendMaildButton_Click(ByVal sender As System.Object, _
                                      ByVal e As System.EventArgs) Handles SendButton.Click
        'sc instance of SmtpClient already created on OnLoad form event
        ' [sc.Host, sc.Port, sc.Credentials stuff ...]

        Dim message As MailMessage
        ' [message filling]

        ' [relevant part : Send or SendAsync]

        ' freedom...
        message.Dispose()
    End Sub
End Class

sc.Send()

Dim userState As String = "plap" 'message.GetHashCode
    AddHandler sc.SendCompleted, AddressOf SendCompletedCallback
    sc.SendAsync(message, userState)

19 janv. 2017 17:15:43 ERROR com.nilhcem.fakesmtp.server.MailSaver -
java.io.EOFException: Pre-mature end of <CRLF>.<CRLF> terminated data
        at org.subethamail.smtp.io.DotTerminatedInputStream.read(DotTerminatedInputStream.java:73) ~[fakeSMTP-2.0.jar:na]
        at org.subethamail.smtp.io.DotUnstuffingInputStream.read(DotUnstuffingInputStream.java:47) ~[fakeSMTP-2.0.jar:na]
        at org.subethamail.smtp.io.DotUnstuffingInputStream.read(DotUnstuffingInputStream.java:76) ~[fakeSMTP-2.0.jar:na]