Is the site hosted locally or remotely?  It seems you might need to
authenticate with a password for the smtp.

Hello Dave,

do u have the right credentials for the SMTP in your web.config?
because as  was noted this could lead u to that exception

---
WBR,
Michael  Nemtsev [.NET/C# MVP] :: blog: http://spaces.live.com/laflour 

"The greatest danger for most of us is not that our aim is too high and we
miss it, but that it is too low and we reach it" (c) Michelangelo

D> I have the following code to send an email and I get this error:
D> [SmtpFailedRecipientException: Mailbox unavailable. The server
D> response was: <someEmail@someHost.com> No such user here]. The error
D> is on at last line below.
D>
D> SmtpClient smtpClient = new SmtpClient();
D> MailMessage message = new MailMessage();
D> MailAddress fromAddress = new
D> MailAddress("myMail@anyHost.com",
D> "POS-eTive Point of
D> Sales.");
D> // host name of server
D> smtpClient.Host = "mail.someHost.com";
D> //Default port will be 25
D> smtpClient.Port = 25;
D> //From address will be given as a MailAddress Object
D> message.From = fromAddress;
D> // To address collection of MailAddress
D> message.To.Add(Email.Text);
D> message.Subject = " auto responder notice.";
D> // Message body content
D> message.Body = "some message";
D> // Send SMTP mail
D> smtpClient.Send(message);

I assume the e-mail address you are trying to send to doesn't exist. Try
another one which exists for sure.

SmtpFailedRecipientException Class
Represents the exception that is thrown when the SmtpClient is not able to
complete a Send or SendAsync operation to a particular recipient.

hth,
Andreas