Hi,
After setting IsBodyHTMl true,you'll have to make the body HTML check the code
string text= "<table><tr><td>EmpId</td><td>Emp name</td><td>age</td></tr><tr><td>value</td><td>value</td><td>value</td></tr></table>"
MailMessage mail = new MailMessage();
mail.To ="me@mycompany.com";
mail.From = "you@yourcompany.com";
mail.Subject = "this is a test email.";
mail.IsBodyHtml=true;
mail.Body = text;
MailAttachment attachment = new MailAttachment( Server.MapPath( "test.txt" ) );
mail.Attachments.Add( attachment );
SmtpMail.SmtpServer = "smtp.gmail.com";