Mass Emailing - Where did my emails go?

I have an application that sends off Newsletters via SMTP located on a web server. It works perfectly for <100 emails, but yesterday, I tried to send one off to over 3,800+ users, but unfortunately, it seemed not to go through.

I have a DataReader that displays each email that it sends it off to (for confirmation purposes) and it looks like it did went off, but no one has received it. I believe I have good exception handling implemented as shown below:

public void Send_Mail(Object sender, System.Web.UI.ImageClickEventArgs e)
 {
 SqlConnection conn = new SqlConnection("my connection string");
 SqlCommand comm = new SqlCommand("my SQL statement, conn);
 SqlDataReader dr;
 MailMessage mailer = new MailMessage();
 mailer.From = txtFrom.Text.Trim();
 mailer.Subject = txtSubject.Text.Trim();
 mailer.Body = txtBody.Text.Trim();
 mailer.BodyFormat = MailFormat.Html;
 try
 {
 conn.Open();
 dr = comm.ExecuteReader(CommandBehavior.CloseConnection);
 while(dr.Read())
 {
 mailer.To = dr[0].ToString();
 lblConfirmation.Text = dr[0].ToString();
 SmtpMail.SmtpServer = "xx.xx.xx.xxx";
 SmtpMail.Send(mailer);
 }
 dr.Close();
 lblConfirmation.Text = "Your message was successfully sent to the following recipients:" ;
conn.Open();
dgrid.DataSource = comm.ExecuteReader(CommandBehavior.CloseConnection);
 dgrid.DataBind();
dr.Close();
 }
 catch(SqlException ex)
 {
 Response.Write("A database-related exception occurred!<br>" + ex.ToString());
 }
 catch(Exception ex)
 {
 Response.Write("A general exception occurred!<br>" + ex.ToString());
 }
 finally
 {
 if(conn.State == ConnectionState.Open)
 {
 conn.Close();
 }
 }
 }

Everything seems the same as with 100 emails as with 3,800 emails, but can't seem to know where my emails went. I did go to (C:\inetput\mailroot) but couldn't find anything near my situation.

Could someone please help me out here? Is there a queue somewhere I don't know about? ASP.NET can handle this type of mass mailings correct?

Any advice will be greatly appreciated.OK, I just learned that the Exchange Server our corporation goes off of DOES NOT allow emailing over 200 users. Ahh, at least I know one part of my problem.

Now, to go around this constraint, I was thinking of setting up a loop and sending emails in chunks of 100 or so and separated by say 5 minutes. Is this good practice? I would like know what everyone else is doing?

Also, I noticed a thread a few months back here (I believe) that someone was attempting something very similar to my situation, but I can't seem to locate that thread anymore. Anyone know what I am talking about?

Your assistance will be greatly appreciated!