平衡点

_ Exim4 のローカル設定[Debian] [Computer] 

Single Exim4 configuration file で設定していたが, サーバ固有の設定ってドコでやるのが御作法なのか, これまでちゃんと調べていなかったのだけれど.

Incidentally, the /etc/exim4/exim4.conf.localmacros file will be read in first, which makes it the ideal place to put any macros you may want to set. Using this file you can control various features (DKIM for example) and still gain the benefits of not touching the debian provided files, so hopefully having more seamless upgrades.

[from:Exim - Debian Wiki]

というわけで, /etc/exim4/exim4.conf.localmacros に書くのが御作法であるようだ.