Linuxdoc Linux Questions
Click here to ask our community of linux experts!
Custom Search

A.3. Options and Settings

The main section of the Exim configuration file (before the first begin keyword) contains various macros, policy controls, and other general settings. Let us start by defining a couple of macros we will use later:


# Define the message size limit; we will use this in the DATA ACL.
MESSAGE_SIZE_LIMIT = 10M

# Maximum message size for which we will run Spam or Virus scanning.
# This is to reduce the load imposed on the server by very large messages.
MESSAGE_SIZE_SPAM_MAX = 1M

# Macro defining a secret that we will use to generate various hashes.
# PLEASE CHANGE THIS!.
SECRET = some-secret

Let us tweak some general Exim settings:


# Treat DNS failures (SERVFAIL) as lookup failures.
# This is so that we can later reject sender addresses 
# within non-existing domains, or domains for which no
# nameserver exists.
dns_again_means_nonexist = !+local_domains : !+relay_to_domains

# Enable HELO verification in ACLs for all hosts
helo_try_verify_hosts = *

# Remove any limitation on the maximum number of incoming
# connections we can serve at one time.  This is so that while
# we later impose SMTP transaction delays for spammers, we
# will not refuse to serve new connections.
smtp_accept_max = 0

# ..unless the system load is above 10
smtp_load_reserve = 10

# Do not advertise ESMTP "PIPELINING" to any hosts.
# This is to trip up ratware, which often tries to pipeline
# commands anyway.
pipelining_advertise_hosts = :

Finally, we will point some Exim policy controls to five ACLs that we will create to evaluate the various stages of an incoming SMTP transaction:


acl_smtp_connect = acl_connect
acl_smtp_helo    = acl_helo
acl_smtp_mail    = acl_mail_from
acl_smtp_rcpt    = acl_rcpt_to
acl_smtp_data    = acl_data