مشكلة في إرسال الإيميل عبر جيميل - GMAIL/SMTP

أنا استخدمت التالي وقد نجح معي

جربه

using System.Net.Mail;
using System.Net;

    	protected void oSendEmail(object sender, EventArgs e)
    	{
        	SmtpClient smtpClient = new SmtpClient();
        	MailMessage message = new MailMessage();
        	try
        	{
            	statusLabel.Text = "";
            	// Prepare two email addresses 
            	MailAddress fromAddress = new MailAddress("YourEmail@gmail.com", "SitePoint");
            	MailAddress toAddress = new MailAddress("OtherEmail@hotmail.com", "You");

            	// Prepare the mail message
            	message.From = fromAddress;
            	message.To.Add(toAddress);
            	message.Subject = "Testing!";
            	message.Body = "This is the body of a sample message";

            	// Set server details
            	smtpClient.Host = "smtp.gmail.com";
            	smtpClient.EnableSsl = true;

            	NetworkCredential NetworkCred = new NetworkCredential();

            	NetworkCred.UserName = "YourEmail@gmail.com";

            	NetworkCred.Password = "YourPassword";

            	smtpClient.UseDefaultCredentials = true;

            	smtpClient.Credentials = NetworkCred;

            	smtpClient.Send(message);

            	statusLabel.Text = "Email sent.";
        	}
        	catch (Exception ex)
        	{
            	// Display error message
            	statusLabel.Text = "Coudn't send the message! \r\n";// +Environment.NewLine + ex.Message;
        	}
    	}

الكود اللي استخدمته للإرسال هو التالي

Sub SendEmail()
        Try
            Dim SmtpServer As New SmtpClient()
            Dim mail As New MailMessage()
            SmtpServer.Credentials = New  _
            Net.NetworkCredential("email@gmail.com", "@password@")
            SmtpServer.Port = 587
            SmtpServer.Host = "smtp.gmail.com"
            mail = New MailMessage()
            mail.From = New MailAddress("mail@gmail.com")
            mail.To.Add(txtTo.Text)
            mail.Subject = txtTitle.Text
            mail.Body = txtBody.Text
            For Each S As String In LstAtts.Items
                mail.Attachments.Add(New Attachment(S))
            Next

            SmtpServer.Send(mail)
            MsgBox("تم إرسال الإيميل بنجاح", MsgBoxStyle.OkOnly, "..")
            DialogResult = Windows.Forms.DialogResult.OK
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub

لكن المشكلة ليست أنه بعمل أو لا يعمل .. المشكلة أنه يعمل على بعض الاجهزة وبعضها لا يعمل عليه!

        Try
            Dim ClientSrv As New SmtpClient("smtp.gmail.com", "587") '25
            ClientSrv.EnableSsl = True
            ClientSrv.UseDefaultCredentials = True
            ClientSrv.Credentials = New NetworkCredential("EMAIL@gmail.com", "PASSWORD")
            Dim MSG As New MailMessage("EMAIL@gmail.com", "ToEmail@hotmail.com","Subject", "Body")

            ClientSrv.Send(MSG)
            MsgBox("تم إرسال الإيميل بنجاح")
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try