Can you send e-mail to people of your Exchange domain (like to yourself) ?

If the answer is yes, your code is working correctly. Now if you try to send e-mails to addresses outside your domain and it fails, it is surely because your Exchange admin stop relaying (which is a protection against spamming).

I sometime use this code to test an installation:

Option Strict On

Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents txtFrom As System.Windows.Forms.TextBox
    Friend WithEvents txtTo As System.Windows.Forms.TextBox
    Friend WithEvents Label2 As System.Windows.Forms.Label
    Friend WithEvents txtSubject As System.Windows.Forms.TextBox
    Friend WithEvents Label3 As System.Windows.Forms.Label
    Friend WithEvents Label4 As System.Windows.Forms.Label
    Friend WithEvents txtBody As System.Windows.Forms.TextBox
    Friend WithEvents txtServer As System.Windows.Forms.TextBox
    Friend WithEvents Label5 As System.Windows.Forms.Label
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.Label1 = New System.Windows.Forms.Label()
        Me.txtFrom = New System.Windows.Forms.TextBox()
        Me.txtTo = New System.Windows.Forms.TextBox()
        Me.Label2 = New System.Windows.Forms.Label()
        Me.txtSubject = New System.Windows.Forms.TextBox()
        Me.Label3 = New System.Windows.Forms.Label()
        Me.txtBody = New System.Windows.Forms.TextBox()
        Me.Label4 = New System.Windows.Forms.Label()
        Me.txtServer = New System.Windows.Forms.TextBox()
        Me.Label5 = New System.Windows.Forms.Label()
        Me.SuspendLayout()
        '
        'Button1
        '
        Me.Button1.Location = New System.Drawing.Point(496, 256)
        Me.Button1.Name = "Button1"
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Send"
        '
        'Label1
        '
        Me.Label1.Location = New System.Drawing.Point(16, 48)
        Me.Label1.Name = "Label1"
        Me.Label1.TabIndex = 1
        Me.Label1.Text = "From"
        '
        'txtFrom
        '
        Me.txtFrom.Location = New System.Drawing.Point(128, 48)
        Me.txtFrom.Name = "txtFrom"
        Me.txtFrom.Size = New System.Drawing.Size(440, 20)
        Me.txtFrom.TabIndex = 2
        Me.txtFrom.Text = "de@compagnie.com"
        '
        'txtTo
        '
        Me.txtTo.Location = New System.Drawing.Point(128, 80)
        Me.txtTo.Name = "txtTo"
        Me.txtTo.Size = New System.Drawing.Size(440, 20)
        Me.txtTo.TabIndex = 4
        Me.txtTo.Text = "a@compagnie.com"
        '
        'Label2
        '
        Me.Label2.Location = New System.Drawing.Point(16, 80)
        Me.Label2.Name = "Label2"
        Me.Label2.TabIndex = 3
        Me.Label2.Text = "To"
        '
        'txtSubject
        '
        Me.txtSubject.Location = New System.Drawing.Point(128, 112)
        Me.txtSubject.Name = "txtSubject"
        Me.txtSubject.Size = New System.Drawing.Size(440, 20)
        Me.txtSubject.TabIndex = 6
        Me.txtSubject.Text = "Sujet"
        '
        'Label3
        '
        Me.Label3.Location = New System.Drawing.Point(16, 112)
        Me.Label3.Name = "Label3"
        Me.Label3.TabIndex = 5
        Me.Label3.Text = "Subject"
        '
        'txtBody
        '
        Me.txtBody.Location = New System.Drawing.Point(128, 144)
        Me.txtBody.Multiline = True
        Me.txtBody.Name = "txtBody"
        Me.txtBody.ScrollBars = System.Windows.Forms.ScrollBars.Vertical
        Me.txtBody.Size = New System.Drawing.Size(440, 104)
        Me.txtBody.TabIndex = 8
        Me.txtBody.Text = "Contenu du message"
        '
        'Label4
        '
        Me.Label4.Location = New System.Drawing.Point(16, 144)
        Me.Label4.Name = "Label4"
        Me.Label4.TabIndex = 7
        Me.Label4.Text = "Body"
        '
        'txtServer
        '
        Me.txtServer.Location = New System.Drawing.Point(128, 16)
        Me.txtServer.Name = "txtServer"
        Me.txtServer.Size = New System.Drawing.Size(440, 20)
        Me.txtServer.TabIndex = 10
        Me.txtServer.Text = "VotreServeurSMTP"
        '
        'Label5
        '
        Me.Label5.Location = New System.Drawing.Point(16, 16)
        Me.Label5.Name = "Label5"
        Me.Label5.TabIndex = 9
        Me.Label5.Text = "Server"
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(576, 294)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.txtServer, _
Me.Label5, Me.txtBody, Me.Label4, Me.txtSubject, Me.Label3, Me.txtTo, Me.Label2, _
Me.txtFrom, Me.Label1, Me.Button1})
        Me.Name = "Form1"
        Me.Text = "Test d'envoi de courriels"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            'Votre message
            Dim objMessage As New System.Web.Mail.MailMessage()
            With objMessage
                .From = txtFrom.Text
                .To = txtTo.Text
                '.Cc=
                '.Bcc=
                .Body = txtBody.Text
                .BodyFormat = Web.Mail.MailFormat.Text
                .Subject = txtSubject.Text
                '.Attachments=
            End With

            'Quel serveur utiliser?
            System.Web.Mail.SmtpMail.SmtpServer = txtServer.Text

            'Envoi du message
            System.Web.Mail.SmtpMail.Send(objMessage)
            objMessage = Nothing
        Catch ex As Exception
            MessageBox.Show(ex.ToString)
        End Try
    End Sub
End Class

>Hi Eric!
>
>This is some what starting get a little anoying! You say that all i have to do is provide the name of our Exchange server and everything should work out? I have tried that and it does not work. I tried it out by name and by IP but it did not work. Any idea what could be wrong?
>
>
>Thanx!
>
>Martin