I found out that I can do that with vacation program.
So, I installed vacation-184.108.40.206-3.i386.rpm, created ~/.vacation.msg with the fallowing content:
Subject: away from my mail
I will not be reading my mail for a while.
Your mail concerning "$SUBJECT"
will be read when I'm back.
Then I created ~/.forward:
\username_who_is_in_vacation, "|/usr/bin/vacation username_who_is_in vacation"
I ran: #/usr/bin/vacation -I
Despite all these, it doesn't work.
I'am using sendmail V8.12.
Do you know why? What can I do?