A long time ago I had found how easy it was to reject messages outright with Postfix that came from non-existent domains. You know… junk from asdflkjuasdlfkjh@imadethisupmyselfanditsnotregisteredanywhere.com
Well, since the mailserver at THIS site runs sendmail I wanted to fix sendmail the same as my home server. My home server is postfix based and uses fetchmail to pull from the website. Since I had the rules set to reject non-existent domains at home it would essentially strand messages in the account here at the website which would then need to be cleaned out manually.