VB.net Windows Forms Failure Sending Mail SMTP Exception

I am getting the following error "Failure Sending Mail: SMTP Exception" in the following code

    Private Sub btnSendNetMail_Click(sender As System.Object, e As Microsoft.Office.Tools.Ribbon.RibbonControlEventArgs) Handles btnSendNetMail.Click
        SendNetMail("murbro9@yahoo.com", "murbro9@yahoo.com", "Test Subject", "", "")
    End Sub


    Public Sub SendNetMail(ByVal MsgFrom As String, ByVal MsgTo As String, ByVal MsgSubject As String, ByVal MsgBody As String, ByVal oAttachment As String)

        Try

            '  Pass in the message information to a new MailMessage

            Dim msg As New Net.Mail.MailMessage(MsgFrom, MsgTo, MsgSubject, MsgBody)

            If oAttachment = "" Then
                'Do nothing
            Else
                msg.Attachments.Add(New System.Net.Mail.Attachment(oAttachment))
            End If



            ' Set the format of the mail message body as HTML
            msg.IsBodyHtml = True
            ' Set the priority of the mail message to normal
            msg.Priority = MailPriority.Normal

            '   Create an SmtpClient to send the e-mail

            ' Dim mailClient As New SmtpClient("105.236.251.36")  '  = local machine IP Address
            Dim mailClient As New SmtpClient(GetIPAddress)  '  = local machine IP Address

            '  Use the Windows credentials of the current User

            mailClient.UseDefaultCredentials = True



            ' Pass the message to the mail server

            mailClient.Send(msg)

            '  Optional user reassurance:

            'MsgBox(String.Format("Message Subject ' {0} ' successfully sent From {1} To {2}", MsgSubject, MsgFrom, MsgTo), "EMail", Windows.Forms.MessageBoxButtons.OK)

            '  Housekeeping

            msg.Dispose()

        Catch ex As FormatException

            MsgBox(ex.Message & " :Format Exception")

        Catch ex As SmtpException

            MsgBox(ex.Message & " :SMTP Exception")

        End Try
    End Sub

    Private Function GetIPAddress() As String
        Try
            Dim strHostName As String
            Dim strIPAddress As String

            strHostName = System.Net.Dns.GetHostName()
            strIPAddress = System.Net.Dns.GetHostByName(strHostName).AddressList(0).ToString()
            GetIPAddress = strIPAddress
        Catch
            MsgBox(Err.Description & " abc4")
        End Try

        '
    End Function