The email user is valid.
I checked the event log. I wonder if I need to use NTLM? I've tried basic and anonymous.
here's the error I see when the registration email is trying to send.
This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server. at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response) at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception) at System.Net.Mail.SmtpClient.Send(MailMessage message) at DotNetNuke.Services.Mail.Mail.SendMail(String MailFrom, String MailTo, String Cc, String Bcc, MailPriority Priority, String Subject, MailFormat BodyFormat, Encoding BodyEncoding, String Body, String Attachment, String SMTPServer, String SMTPAuthentication, String SMTPUsername, String SMTPPassword, Boolean SMTPEnableSSL)