I am having issues sending a confirmation email to user after registration. I've tried 2 Hotmail email and I got Mailbox unavailable error. It show "System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: <theEmail@hotmail.com> No such user here". I read some threads, but I couldn't get an answer. The first time, I used my own Hotmail email, and the second time I used my brother's email. I got the same error message. I successfully logged into my account on mail.mydomain.com with the username firstname.lastname@example.org, and from there I can send an email to the Hotmail account. But from my Winhost hosted website, It does not work. Can anyone provide help? Here is my web.config <system.net> <mailSettings> <smtpfrom="email@example.com"> <networkhost="mail.mydomainname.com"password="mypa$$w0rd" userName="firstname.lastname@example.org"defaultCredentials="true" /> </smtp> </mailSettings> </system.net> ================== Here is the VB code behind Dim TextMsg AsString = "Thanks for registering..." Dim SenderEmail AsString = Trim(txtUserEmail.Text) Dim SenderName AsString = Trim(txtName.Text) Dim MailMsg AsNewMailMessage() MailMsg.BodyEncoding = Encoding.Default MailMsg.Subject = "Welcome to..." MailMsg.Body = TextMsg MailMsg.Priority = MailPriority.High MailMsg.IsBodyHtml = True MailMsg.From = NewMailAddress("email@example.com", "Domain Moto") MailMsg.To.Add(NewMailAddress(SenderEmail, SenderName)) 'SmtpClient to send the mail message Dim SmtpMail AsNewSmtpClient SmtpMail.Send(MailMsg) ================ After I enable debug=true in the web.config, it pointed out the line SmtpMail.Send(MailMsg). I don't know what it wrong. I can see in the database that the user has been added, but still I can't send a confirmation email to Hotmail account.