Thanks to every one who replied to my previous message. I have
now found the problem.
I have both exim and mercury set to handle mail for pcfe.ac.uk as
local. Mercury was complaining because the user mailer-daemon
did not exist on our NDS. I simply created a new NDS account with
the name mailer-daemon and everything is working fine.
Thanks again.
Gordon Carn BSc
Postmaster
Plymouth College of Further Education
Kings Road
Devonport
Plymouth
Devon
PL1 5QG
England