Synopsis

You want to use ALOHA load balancer in front of a mail platform, relying on HAProxy to achieve load-balancing.
You mail platform delivers IMAP acts as a SMTP relay for your users.
You want your users to use the same server for both protocols in order to take advantage of different caches level (FS cache, authentication, etc…)

Configuration

The HAProxy configuration below explain how to force the SMTP relay for IMAP connected users.
Users relaying mail through SMTP will be connected to any server in the farm using round robin.

frontend ft_smtp
  bind :25
  mode tcp
  default_backend bk_smtp

frontend ft_imap
  bind :143
  mode tcp
  default_backend bk_imap

backend bk_smtp
  mode tcp
  balance roundrobin
  stick match src table bk_imap
  server s1 192.168.1.1:25 check
  server s2 192.168.1.2:25 check

backend bk_imap
  mode tcp
  # imap connections are usually long
  balance leastconn
  stick store-request src
  stick-table type ip size 200k expire 30m
  server s1 192.168.1.1:143 check
  server s2 192.168.1.2:143 check

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