I would sign up to a service like SendGrid.com and send emails through them. Keep the burden of sending emails off your network.
Here is an example of the code i would use:
var smtp = new SmtpClient
{
Host = "smtp.sendgrid.net",
DeliveryMethod = SmtpDeliveryMethod.Network,
UseDefaultCredentials = false,
Port = 25,
Credentials = new NetworkCredential("name@example.com", "password")
};
MailMessage thisMessage = new MailMessage(fromAddress, toAddress);
thisMessage.IsBodyHtml = true;
thisMessage.Subject = "Title Here";
thisMessage.Body = "Sample Body";
foreach (DataRow thisEmail in dtEmails.Rows)
{
thisMessage.Bcc.Add(thisEmail["AccountEmail"].ToString());
if (thisMessage.Bcc.Count > 500)
{
smtp.Send(thisMessage);
thisMessage.Bcc.Clear();
}
}
smtp.Send(thisMessage);