Smtp Mail发送超时

Question

Imports System.Web
Imports System.IO
Imports System.Net.Mail
Public Class Form1

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim num As Integer = 0
    For intLoopIndex = 0 To Convert.ToInt32(TextBox5.Text)
        Dim mail As New MailMessage
        Dim SmtpServer As New SmtpClient
        SmtpServer.Credentials = New Net.NetworkCredential(TextBox3.Text, TextBox4.Text)
        SmtpServer.Port = 465
        SmtpServer.Host = "smtp-relay.gmail.com"
        SmtpServer.EnableSsl = False

        If ComboBox1.SelectedItem = "AT&T" Then
            mail.To.Add(TextBox1.Text + "@txt.att.net")
            mail.From = New MailAddress(TextBox3.Text)
            mail.Subject = TextBox2.Text
            mail.Body = RichTextBox1.Text
            SmtpServer.Send(mail) '<-- times out here

        ElseIf ComboBox1.SelectedItem = "7-11 Speakout" Then
            mail.To.Add(TextBox1.Text + "@cingularme.com")
            mail.From = New MailAddress(TextBox3.Text)
            mail.Subject = TextBox2.Text
            mail.Body = RichTextBox1.Text
            SmtpServer.Send(mail) '<-- times out here
        End If
        num = num + 1
        Label1.Text = num
    Next intLoopIndex
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Process.Start("http://www.fonefinder.net/")
End Sub
End Class

当我运行此代码时，我在尝试发送电子邮件时收到错误消息。当我运行程序时，我得到一个通用的超时错误，例如，Verizon。我正在使用GMail帐户的正确登录详细信息，我已经尝试了我在网上找到的每个修复程序。它适用于我拥有的每个运营商（邮件服务器）。