After setting the custom errors to off, the following is the error:
Mailbox unavailable. The server response was: <firstname.lastname@example.org> No such user here
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
</br>Exception Details: System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: <email@example.com> No such user here
You mentioned username, password and post for my smtp server, where do I make these changes please?
Thank you very much indeed for your prompt responses.