Hi anyone have an explanation for the following error inthe event log after adding a new user?

Cheers,

Colin

AssemblyVersion: 04.03.06
PortalID: 0
PortalName: My Portal
UserID: 1
UserName: Masterhost
ActiveTabID: 42
ActiveTabName: User Accounts
RawURL: /Admin/UserAccounts/tabid/42/ctl/Edit/mid/350/UserId/3/Default.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.mydomain.com/Admin/UserAccounts/tabid/42/ctl/Edit/mid/350/UserId/3/Default.aspx
UserAgent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.1.4322; FDM; .NET CLR 2.0.50727; InfoPath.2)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 90d19c18-3eec-4cf5-9ac9-90d0a3af4887
InnerException: Mailbox name not allowed. The server response was: sorry, that domain isn't allowed to be relayed thru this MTA (#5.7.1)
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method: System.Net.Mail.SmtpTransport.SendMail
StackTrace:
Message: System.Net.Mail.SmtpFailedRecipientException: Mailbox name not allowed. The server response was: sorry, that domain isn't allowed to be relayed thru this MTA (#5.7.1) 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)