Imports System.Text.RegularExpressions
Public Class Form1
  Inherits System.Windows.Forms.Form

Vom Windows Form Designer generierter Code

  Private Sub Button1_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button1.Click

    Dim sLine As String
    Dim i As Integer

    If CheckEMail(TextBox1.Text) = False Then
      MsgBox("Bitte eine gültige EMail-Adresse eingeben!", _
            MsgBoxStyle.Exclamation)
      Exit Sub
    End If

    sLine = Replace(TextBox3.Text, vbNewLine, "%0A")

    Process.Start("mailto:" & TextBox1.Text & _
                "?subject=" & TextBox2.Text & _
                "&body=" & sLine)
  End Sub

  Private Function CheckEMail(ByVal mail As String) As Boolean
    Dim myRegex As Regex = New Regex( _
          "^[\w\.\-]+@([\w\-]+\.)*[\w\-]{2,63}\.[a-zA-Z]{2,4}$")

    If Not myRegex.IsMatch(TextBox1.Text) Then
      Return False
    Else
      Return True
    End If
  End Function

  Private Sub Button2_Click(ByVal sender As System.Object, _
          ByVal e As System.EventArgs) Handles Button2.Click
    Me.Close()
  End Sub
End Class