This is meant to be a very simple implementation. There's no whitelist, though it's easy to add, and very little error checking — though I've found no need so far. It is based on work by Evan Harris and more specifically, on an implementation using PostgreSQL by Tollef Fog Heen.
Create a table for the greylist:
CREATE TABLE exim_greylist (
id integer NOT NULL auto_increment,
relay_ip varchar(64),
from_domain varchar(255),
block_expires datetime NOT NULL,
record_expires datetime NOT NULL,
origin_type enum('MANUAL','AUTO') NOT NULL default 'AUTO',
create_time datetime NOT NULL,
PRIMARY KEY (id)
);
Give privileges as proper.
In the main part of your exim.conf
file, add some macros:
GREYLIST_TEST = SELECT CASE \
WHEN now() - block_expires > 0 THEN 2 \
ELSE 1 \
END \
FROM exim_greylist \
WHERE relay_ip = '${quote_mysql:$sender_host_address}' \
AND from_domain = '${quote_mysql:$sender_address_domain}'
GREYLIST_ADD = INSERT INTO exim_greylist (relay_ip, from_domain, \
block_expires, record_expires, create_time) \
VALUES ( '${quote_mysql:$sender_host_address}', \
'${quote_mysql:$sender_address_domain}', \
DATE_ADD(now(), INTERVAL 5 MINUTE), \
DATE_ADD(now(), INTERVAL 7 DAY), \
now() \
)
And an SQL server login if you don't have one:
hide mysql_servers = [server1]/[db]/[user]/[password]:\
[server2]/[db]/[user]/[password]
In the ACL controlling the response to the RCPT command, put this line near the top, since it has no action but to set a variable.
warn set acl_m2 = ${lookup mysql{GREYLIST_TEST}{$value}{0}}
And after rules for all mail that you always accept, like postmaster addresses or mail from trusted relays, add the following.
defer message = Greylisted - please try again a little later.
condition = ${if eq{$acl_m2}{0}{1}}
condition = ${lookup mysql{GREYLIST_ADD}{yes}{no}}
defer message = Greylisted - please try again shortly.
condition = ${if eq{$acl_m2}{1}{1}}