If you are receiving the error ‘Administrative prohibition’ in your Exim error logs and what to find out more details about this error, add the following line to your exim.conf file(usually located in /etc/exim/exim.conf).

   smtp_return_error_details=yes

After doing so, restart the exim mail server(/etc/init.d/exim restart) and watch for the error to occur again.  Once it does, exim should provide more information as to why this error is occuring.