I got good workaround for balancing smtp outgoing from postfix mailing list archives(not using expensive real load balancer). suppose we have 4 smtp servers for outgoing email, and we need to configure/load balance like this:
+------------+
| |
+----------> smtp backend a -------->| |
| | |
clients --------> smtp lb -----> smtp backend b -------->| Intenet |
| | |
+----------> smtp backend c -------->| |
| |
+------------+
Here’s the configuration :
Postfix section
main.cf (smtp lb/load balancer)
/etc/postfix/main.cf: relayhost = example.com
Dns sections
named.conf
/etc/named.conf:
options {
directory "/var/named/data";
};
zone "example.com" in {
type master;
file "example.com";
};
example.com zone file
/var/named/data/example.com
$TTL 2D;
@ IN SOA a.ns.example.com hostmaster.example.com (
1 ; Serial
10800 ; Refresh after 3 hours
3600 ; Retry after 1 hour
604800 ; Expire after 1 week
3600 ) ; Minimum TTL of 1 hour
@ IN NS a.ns
@ IN NS b.ns
a.ns IN A 192.0.2.1
b.ns IN A 192.0.2.2
@ IN MX 0 a.mx
@ IN MX 0 b.mx
@ IN MX 0 c.mx
a.mx IN A 192.0.2.3
b.mx IN A 192.0.2.4
c.mx IN A 192.0.2.5
By default relayhost(in main.cf) will listing all available mx on example.com and randomly shuffles mx with equal preference(Postfix client makes a random selection between equal-preference MX hosts), in this case these mx are our smtp backend for balancing outgoing mail.
Source : postfix manual (relayhost)
Victor Duchovni (postfix-users mailing list)
If there’s additional interest in load balancing take a look at the affordables offered by companies like KEMP Technologies or the large enterprise ones offered by companies like F5 networks.
http://www.kemptechnologies.com/?utm_source=blog&utm_medium=pv&utm_content=zs&utm_campaign=home
Hello,
We have setup this similar setup in our server for email marketing. However, the email are bounced back with relay access is denied. We need a bounce back emails. Can you tell me how can we fix this?
The postfix have a internal algorithm that per default randomize the order of equal-preference MX host addresses. Modifying the parameter “smtp_randomize_addresses” to “no” the postfix will use all mx host list sequentially.
sure, that should do the job done in round robin fashion 😀