use below function
public bool SendEmialWithSecure(string ToEmailId, string FromEmailId, string FromName, string SenderEmailId,
string SenderName, string Subject, string MailBody, string SMTPHost, Int32 SMTPPort,
string CredentialEmailId, string CredentialPassword, string strAttachment)
{
System.Net.Mail.MailMessage ResetPassMail = new System.Net.Mail.MailMessage();
SmtpClient SmtpServer = new SmtpClient();
ResetPassMail.To.Add(new MailAddress(ToEmailId));
ResetPassMail.From = new MailAddress(FromEmailId, FromName);
ResetPassMail.Sender = new MailAddress(SenderEmailId, SenderName);
ResetPassMail.Subject = Subject;
ResetPassMail.IsBodyHtml = true;
ResetPassMail.Body = MailBody;
ResetPassMail.Priority = System.Net.Mail.MailPriority.High;
Attachment attach = new Attachment(strAttachment);
ResetPassMail.Attachments.Add(attach);
SmtpServer.Host = SMTPHost;
SmtpServer.Port = SMTPPort;
SmtpServer.Credentials = new NetworkCredential(CredentialEmailId, CredentialPassword);
SmtpServer.DeliveryMethod = SmtpDeliveryMethod.Network;
try
{
SmtpServer.Send(ResetPassMail);
return true;
}
catch (Exception ex)
{
throw ex;
}
}