Set limits for the "low priority" outbound mail transport

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

@@ -43,11 +43,11 @@ 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 ${pcre}transport.pcre ${indexed}mailman_transport
+relay_recipient_maps = ${ldap}all-recipients ${indexed}transport ${indexed}mailman_transport
 relay_destination_recipient_limit = 1
 
 # Send each message to its target backend.
-transport_maps = ${ldap}all-recipients ${indexed}transport ${indexed}mailman_transport
+transport_maps = ${pcre}transport.pcre ${ldap}all-recipients ${indexed}transport ${indexed}mailman_transport
 
 # resolve aliases
 virtual_alias_maps = ${indexed}virtual ${ldap}aliases
@@ -55,7 +55,9 @@ 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_recipient_limit = 1
 smtp_lowpri_destination_concurrency_limit = 2
+smtp_lowpri_destination_rate_delay = 2s
 
 # SSL configuration (outbound).
 smtp_tls_security_level = may