This is an old revision of the document!

Version 1 -- DNS based

in update-exim4.conf.conf

dc_relay_domains='@mx_secondary'

Version 2 -- runtime config

in CONFDIR/virtual a file (or directory) per domain named after the domain and in main/01_exim4-config_listmacrosdefs

-domainlist relay_to_domains = MAIN_RELAY_TO_DOMAINS
+domainlist relay_to_domains = MAIN_RELAY_TO_DOMAINS : dsearch;CONFDIR/secondary