Sometimes you have to slow down your mail delivery for some destinations or you might want to push out more mails for a certain server as it’s inside your LAN without being unkind to other people. Here’s a way of doing it:

The main.cf file of our postfix installation is the place where we define a new transport map and an according speed limit. As I am slowing down things here, the name of our test transport will be ‘snailmail’ – so here we go:

— main.cf

transport_maps = hash:/etc/postfix/transport
snailmail_destination_concurrency_limit = 1

The Transport map file itself now contains the domain(s) we’re changing the limits for by assigning the new transport service:

— /etc/postfix/transport

domain.com snailmail:

Finally we’re hacking our master.cf file for defining our snailmail service to be able to make use of it:
— master.cf

snailmail unix – – n – 5 smtp

The results we’re expecting are now, that all mail traffic regarding domain.com (we’ve used that in the transport map file – remember?) is using our new delivery service. But wait – we haven’t generated the hash file for the transport map. Running postmap /etc/postfix/transport does so. Now we’re set up for the restart.

Believe it or not – we’re done – and it wasn’t even complicated.