sender_dependent_default_transport_maps =
  randmap:{relay1,relay2,relay3,relay4,relay5}
transport_maps = hash:/etc/postfix/transport

# Throttle limit policy mail (global)
smtp_destination_concurrency_limit = 4
smtp_extra_recipient_limit = 2

# Polite policy
polite_destination_concurrency_limit = 3
polite_destination_rate_delay = 0
polite_destination_recipient_limit = 5

# Turtle policy
turtle_destination_concurrency_limit = 2
turtle_destination_rate_delay = 1s
turtle_destination_recipient_limit = 2

relay1     unix  -       -       n       -       -       smtp
  -o smtp_bind_address=IP1
  -o smtp_helo_name=foo1.bar.com
  -o syslog_name=relay1
relay2     unix  -       -       n       -       -       smtp
  -o smtp_bind_address=IP2
  -o smtp_helo_name=foo2.bar.com
  -o syslog_name=relay2
relay3     unix  -       -       n       -       -       smtp
  -o smtp_bind_address=IP3
  -o smtp_helo_name=foo3.bar.com
  -o syslog_name=relay3
relay4     unix  -       -       n       -       -       smtp
  -o smtp_bind_address=IP4
  -o smtp_helo_name=foo4.bar.com
  -o syslog_name=relay4
relay5     unix  -       -       n       -       -       smtp
  -o smtp_bind_address=IP5
  -o smtp_helo_name=foo5.bar.com
  -o syslog_name=relay5
polite unix - - n - - smtp
turtle unix - - n - - smtp