One of my users wants to be able to send out a newsletter every month to about 1200 recipients (and yes, it's double opt-in, no spam, easily unsubscribable). This turned me to custom config postfix using Code: smtp_destination_concurrency_limit = 2 smtp_destination_rate_delay = 1s smtp_extra_recipient_limit = 10 in main.cf I then wanted to use a transport mapping as described here, transport_maps = hash:/etc/postfix/transport but I see ISPConfig already uses virtual transport_maps in main.cf. Is there an easy way to implement options like these below (in ispconfig)? Code: polite unix - - n - - smtp turtle unix - - n - - smtp in master.cf and a /etc/postfix/transport file with Code: gmail.com polite: yahoo.com polite: hotmail.com turtle: outlook.com turtle: live.nl turtle: live.fr turtle: orange.fr turtle: xs4all.nl polite: and then in main.cf add Code: polite_destination_concurrency_limit = 2 polite_destination_rate_delay = 0 polite_destination_recipient_limit = 5 turtle_destination_concurrency_limit = 1 turtle_destination_rate_delay = 3s turtle_destination_recipient_limit = 2