@Joe Davis

I do have a site email from address setup.

This is the error from the log:

System.Net.Mail.SmtpException: Mailbox unavailable. The server response was: 5.7.1 Client does not have permissions to send as this sender
at System.Net.Mail.MailCommand.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 mojoPortal.Net.Email.SendEmailNormal(SmtpSettings smtpSettings, String from, String replyTo, String to, String cc, String bcc, String subject, String messageBody, Boolean html, String priority, String[] attachmentPaths, String[] attachmentNames)

I have seen this error before when programming custom ASP.Net websites to work with exchange. I have to set default credentials to false in the network section of the stmp mail settings. Is there a way to do this in the "site email" settings.

@Joe Audette

I have specified this too.

To give you more information the server used to allow open relay. When this was up and running  the sites email worked great. They have since locked that away and the email failed in both site email and smtp. After switching to use authentication in the smtp settings section the password resets work and will send a valid email. In order to do that I had to set defaultCredentials to be false. Is there a way to do this in the site email settings?

Thanks for the help

Justin