Deterring mail relay attempts

[Alan Chandler <alan@chandlerfamily.org.uk>]

I have just moved my mail server (exim4 split config based) from one 
machine to another, and in doing so started examining the logs.  I am 
being hit with multiple attempts to relay - several a second.  They come 
in bursts from one host, then come from somewhere else.

I would like to put some for of inconvenient barrier up so perhaps they 
stop bothering me.

What is a good way of deterring them?

I've added

delay = 10s

in conf.d/acl/30_exim4-config_check_rcpt

thus:-

# Insist that any other recipient address that we accept is either in one of
# our local domains, or is in a domain for which we explicitly allow
# relaying. Any other domain is rejected as being unacceptable for relaying.
  require
    message = relay not permitted
    domains = +local_domains : +relay_to_domains
    delay = 10s


Does this hang on to the incoming connection for 10 seconds? Is this a 
mini teergrube?  Is 10s a sensible figure?




--
Alan Chandler
http://www.chandlerfamily.org.uk