[bozordzh]

Как эту задачу можно реализовать в postfix? »

в постфиксе aliases работают так же как в шлимыле
http://www.postfix.org/aliases.5.html
|command Mail is piped into command. Commands that contain special characters, such as whitespace, should be enclosed between double quotes. See local(8) for details of delivery to command. When the command fails, a limited amount of command output is mailed back to the sender. The file /usr/include/sysexits.h defines the expected exit status codes. For example, use "|exit 67" to simu- late a "user unknown" error, and "|exit 0" to implement an expensive black hole.