Add a slow (low-concurrency) outbound transport

roles/mail/templates/postfix-out/main.cf

@@ -3,6 +3,7 @@
 {% include "main.cf.base.j2" %}
 
 ldap = proxy:ldap:/etc/postfix/ldap/
+pcre = pcre:${config_directory}/
 
 mynetworks = 127.0.0.0/8 [::1]/128 {% for o in net_overlays %}{{ o.network }} {% endfor %}
 
@@ -42,7 +43,7 @@ smtpd_timeout = 1200s
 # "smtp" transport for outbound mail (bounces, ...). The latter
 # won't starve the former of delivery agent slots.
 relay_domains = ${indexed}domains cdb:/etc/postfix/domains-auto
-relay_recipient_maps = ${ldap}all-recipients ${indexed}transport ${indexed}mailman_transport
+relay_recipient_maps = ${ldap}all-recipients ${indexed}transport ${pcre}transport.pcre ${indexed}mailman_transport
 relay_destination_recipient_limit = 1
 
 # Send each message to its target backend.
@@ -54,6 +55,7 @@ virtual_alias_maps = ${indexed}virtual ${ldap}aliases
 # Concurrency tuning for "relay" and "smtp" transport.
 relay_destination_concurrency_limit = 20
 default_destination_concurrency_limit = 20
+smtp_lowpri_destination_concurrency_limit = 2
 
 # SSL configuration (outbound).
 smtp_tls_security_level = may

roles/mail/templates/postfix-out/master.cf

@@ -19,6 +19,7 @@ flush     unix  n       -       y       1000?   0       flush
 proxymap  unix  -       -       n       -       -       proxymap
 proxywrite unix -       -       n       -       1       proxymap
 smtp      unix  -       -       y       -       -       smtp
+smtp-lowpri unix  -       -       y       -       -       smtp
 relay     unix  -       -       y       -       -       smtp
         -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
         -o smtp_host_lookup=native

roles/mail/templates/postfix-out/transport.pcre

+# Send high-volume, high-spam traffic onto the lower-priority
+# smtp transport.
+/(yahoo|hotmail|live)(\.[a-z]{2,3}){1,2}$/ smtp-lowpri:
+/tiscali\.it$/ smtp-lowpri: