Noteable feature outline of the 4.2.3 exim.conf:

- BlockCracking for smtp-auth connections:
	wget -O /etc/exim.blockcracking.conf http://files1.directadmin.com/services/exim.blockcracking.conf.1.0
	wget -O /etc/exim.blackcracking.variables http://files1.directadmin.com/services/exim.blockcracking.variables.1.0

- Per-User blocking for outbound messages:
For script sends (using acl_script) and smtp-auth sends.
It will figure out which system User this is, and if that user is in this file
/etc/virtual/blacklist_usernames
they cannot send emails.
Script based sends (eg php mail()) are dropped and logged to mainlog, so the user won't know.
But smtp based sends give a nice drop message.

- acl_check_auth to only allow 1 AUTH attempt per connection
It will drop the connection if 2 AUTH attempts are made.

- misc. HELO checks
    - reject HELO IPs
    - deny ylmf-pc if port 25 (very common brute force host)
    - HELO host must not be a local domain.

- acl_not_smtp = acl_script: Script based ACL
    - Limit check (/etc/virtual/limit, limit_username) enforced, else dropped.
    - /etc/virtual/blacklist_usernames checked, dropped if matched.

- Limit check in ACL for authenitcated users, can now provide proper message, rather than password error.

- Separate from the main BlockCracking, a max of 3 failed recipients per connection, else drop with message.

- Incoming mail for suspended local domains will show a message about the suspended domain, and to try later.

- RBL blocking if /etc/virtual/use_rbl_domains filled or linked to "domains"
    http://help.directadmin.com/item.php?id=142

- Spam blocking with SpamAssassin:
    http://help.directadmin.com/item.php?id=36

- Outbound DKIM signing:
    http://www.directadmin.com/features.php?id=1189

- ClamAV:
    http://help.directadmin.com/item.php?id=370