Urgent:Asp.Net 3.5 Is there any limitation for sending message? Email delivery is failing when message is little large

Question

Hi Experts! In the asp.net 3.5, C# I am using Text box with multiline property. I am using smtp to send the email. SmtpClient smtpClient = new SmtpClient(); MailMessage message = new MailMessage(); I am filling up all other values like To, Cc etc., and then getting the textbox text to fill the message body: message.Body = txtboxmessage.Text.ToString(); I observe that when the textbox has very less lines of text, it sends mail successfully. However, when it cosists of more lines of text, it fails. Can anyone advise me how to overcome this problem? Also, please advise how to create email in such way that HTML markup can be added to the message (just like gmail or yahoo or anyother general emails)? Appreciate quick responses. Thanks