Sending mail in c#.net

Hi,

I want to send an email from c#.net code. I have searched it on internet. I found some of the examples and coded according to them. But it gives the following error:

SmtpFailedRecipientException was unhandled by user code:

Mailbox unavailable. The server response was: 5.7.1 Unable to relay for faisal@etexsolutions.com

Below is my code:
MailMessage msgmail = new MailMessage();
msgmail.From = new MailAddress(TextBox2.Text);
msgmail.To.Add(new MailAddress(TextB ...