Florian's weblog

Orange sadly limits inbound connexion to it’s MX to 1 connexion per IP, which is a total pain in the ass when you try to deliver newsletter, or manage a MTA.

Here is a sample log from their MX: Jul 4 10:42:42 smtp.example.com postfix/smtp[32347]: 0123456789: host smtp-in.orange.fr[193.252.22.65] refused to talk to me: 421 mwinf5c34 ME Trop de connexions, veuillez verifier votre configuration. Too many connections, slow down. OFR004_104 [104]

However, since they won’t change anything, we have to take mesures, here’s what you can do if you run postfix: you have to set a per-destination concurrency limit.

• /etc/postfix/main.cf

Identify or configure the transport_maps file:

transport_maps = hash:/etc/postfix/transport

• /etc/postfix/transport

Now, overrides the default transport for Orange (and all of it’s related domains) in the transport maps file

orange.fr     orange:
wanadoo.fr    orange:

Then, use postmap /etc/postfix/transport to generate transport.db

• /etc/postfix/master.cf

You have to configure the new transport “orange” not to fork (maxproc=1) with this line in master.cf:

# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
orange    unix  -       -       n       -       1       smtp

You can now reload postfix and use ps(1) to verify that there only is one “orange” process at a time while delivering emails to Orange users:

postfix  32618 32471  0 17:07 ?        00:00:00 smtp -t unix -u
postfix  32619 32471  0 17:07 ?        00:00:00 smtp -t unix -u
[...]
postfix  32672 32471  0 17:15 ?        00:00:00 smtp -l -n orange -t unix -u

[1] Source: http://www.dj-j.net/waka/Linux:Administration_Postfix