Vacation for non-existant users?

[Do Duc Huy]

Hi all mail administrators!
I use postfix and cyrus for my email system. Everything are Ok, thank for
Opensource community for such greate products. Now, I want to setup my
system to send notification when user email was delivered. (If user email
have "Return-Receipt-To:" field ofcourse). Is there anyone can tell me what
to do. I 'v searching in Internet for some howto document about this
question but havenot found yet.
Thanks for any idea
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Do Duc Huy
Centre for Development Infomation  Technology - CDIT
The 4th floor VCCI buiding #9 Dao Duy Anh Str. Dong Da Dstr. Hanoi
Tel: 84-04-5742879