Try This code .... it works with me ...
Imports System
Imports System.Net.Mail
#Region "Declarations"
' message elements
Private mMailServer As String
Private mTo As String
Private mFrom As String
Private mMsg As String
Private mSubject As String
#End Region
#Region "Methods"
Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
' set up the carriers list - this is a fair list, you may wish to
' research the topic and add others, it took a while to generate this
' list...
cboCarrier.Items.Add("@itelemigcelular.com.br")
cboCarrier.Items.Add("@message.alltel.com")
cboCarrier.Items.Add("@message.pioneerenidcellular.com")
cboCarrier.Items.Add("@messaging.cellone-sf.com")
cboCarrier.Items.Add("@messaging.centurytel.net")
cboCarrier.Items.Add("@messaging.sprintpcs.com")
cboCarrier.Items.Add("@mobile.att.net")
cboCarrier.Items.Add("@mobile.cell1se.com")
cboCarrier.Items.Add("@mobile.celloneusa.com")
cboCarrier.Items.Add("@mobile.dobson.net")
cboCarrier.Items.Add("@mobile.mycingular.com")
cboCarrier.Items.Add("@mobile.mycingular.net")
cboCarrier.Items.Add("@mobile.surewest.com")
cboCarrier.Items.Add("@msg.acsalaska.com")
cboCarrier.Items.Add("@msg.clearnet.com")
cboCarrier.Items.Add("@msg.mactel.com")
cboCarrier.Items.Add("@msg.myvzw.com")
cboCarrier.Items.Add("@msg.telus.com")
cboCarrier.Items.Add("@mycellular.com")
cboCarrier.Items.Add("@mycingular.com")
cboCarrier.Items.Add("@mycingular.net")
cboCarrier.Items.Add("@mycingular.textmsg.com")
cboCarrier.Items.Add("@o2.net.br")
cboCarrier.Items.Add("@ondefor.com")
cboCarrier.Items.Add("@pcs.rogers.com")
cboCarrier.Items.Add("@personal-net.com.ar")
cboCarrier.Items.Add("@personal.net.py")
cboCarrier.Items.Add("@portafree.com")
cboCarrier.Items.Add("@qwest.com")
cboCarrier.Items.Add("@qwestmp.com")
cboCarrier.Items.Add("@sbcemail.com")
cboCarrier.Items.Add("@sms.bluecell.com")
cboCarrier.Items.Add("@sms.cwjamaica.com")
cboCarrier.Items.Add("@sms.edgewireless.com")
cboCarrier.Items.Add("@sms.hickorytech.com")
cboCarrier.Items.Add("@sms.net.nz")
cboCarrier.Items.Add("@sms.pscel.com")
cboCarrier.Items.Add("@smsc.vzpacifica.net")
cboCarrier.Items.Add("@speedmemo.com")
cboCarrier.Items.Add("@suncom1.com")
cboCarrier.Items.Add("@sungram.com")
cboCarrier.Items.Add("@telesurf.com.py")
cboCarrier.Items.Add("@teletexto.rcp.net.pe")
cboCarrier.Items.Add("@text.houstoncellular.net")
cboCarrier.Items.Add("@text.telus.com")
cboCarrier.Items.Add("@timnet.com")
cboCarrier.Items.Add("@timnet.com.br")
cboCarrier.Items.Add("@tms.suncom.com")
cboCarrier.Items.Add("@tmomail.net")
cboCarrier.Items.Add("@tsttmobile.co.tt")
cboCarrier.Items.Add("@txt.bellmobility.ca")
cboCarrier.Items.Add("@typetalk.ruralcellular.com")
cboCarrier.Items.Add("@unistar.unifon.com.ar")
cboCarrier.Items.Add("@uscc.textmsg.com")
cboCarrier.Items.Add("@voicestream.net")
cboCarrier.Items.Add("@vtext.com")
cboCarrier.Items.Add("@wireless.bellsouth.com")
End Sub
Private Sub btnSend_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click
' Collect user input from the form and stow content into
' the objects member variables
mTo = Trim(txtPhoneNumber.Text) &
Trim(cboCarrier.SelectedItem.ToString())
mFrom = Trim(txtSender.Text)
mSubject = Trim(txtSubject.Text)
mMailServer = Trim(txtMailServer.Text)
mMsg = Trim(txtMessage.Text)
' Within a try catch, format and send the message to
' the recipient. Catch and handle any errors.
Try
Dim message As New MailMessage(mFrom, mTo, mSubject, mMsg)
Dim mySmtpClient As New SmtpClient(mMailServer)
mySmtpClient.UseDefaultCredentials = True
mySmtpClient.Send(message)
MessageBox.Show("The mail message has been sent to " &
message.To.ToString(), "Mail", MessageBoxButtons.OK,
MessageBoxIcon.Information)
Catch ex As FormatException
MessageBox.Show(ex.StackTrace, ex.Message, MessageBoxButtons.OK,
MessageBoxIcon.Error)
Catch ex As SmtpException
MessageBox.Show(ex.StackTrace, ex.Message, MessageBoxButtons.OK,
MessageBoxIcon.Error)
Catch ex As Exception
MessageBox.Show(ex.StackTrace, ex.Message, MessageBoxButtons.OK,
MessageBoxIcon.Error)
End Try
End Sub
Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles btnExit.Click
' Upon user’s request, close the application
Application.Exit()
End Sub
#End Region