Extending my last suggestion, because I more carefully re-read the requirement:
> We need to send a 550 error to several senders even though the recipient
> email address is, in fact, valid. This is because the recipient does
> not want to receive any email from the sender and wishes them to think
> that their email does not exist on our receiving servers.
How about this ?
acl_check_rcpt:
deny message = [2C03] Unknown email address $local_part@$domain.
recipients = [email protected]
senders = EXDIR/jonny.unwanted
EXDIR is a predefined variable pointing to the location of Exim data files.
jonny.unwanted contains
[email protected]
fred@junk,com
--
Paul.
England,
EU.
--
## List details at https://lists.exim.org/mailman/listinfo/exim-users
## Exim details at http://www.exim.org/
## Please use the Wiki with this list - http://wiki.exim.org/