I am havin trouble with my auto mail from DNN and dont know what to make of it. I am getting new user sign-up notifications to my admin email but users are not receiving appropriate emails such as for verrifying email address.
I dont understand why one mail out works but the other doesnt

Thanks for the help

here is the error in my event viewer

DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: df654e8d-d866-4d98-8ebf-56762e07ec8c
InnerException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Net.Mail.SmtpTransport.SendMail
StackTrace:
Message: System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay 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)

Thanks for the reply.

I am really lost when it comes to this. The relay was working one day then not the next. my set up is as follows. 
My domain is on Godaddy, it is pointed to my server. the email account is on godaddy. our server is using the godaddy relay in an exchange server account. 
This is frustratng because like I said it worked two days ago, then ....kaboom

Thanks to anyone who can provide further insight on this problem