I didn't find any info about installation of zimbra on Debian 7.

I have chcecked if it's possible, and here is my info based on history.

Finnally I have stayed on Ubuntu 12.04.

The trick was to get libgmp3c2 form squeeze, and only new libc6-dev form testing (without updating the rest) <- this may be changing since packet versions are updating
Ig I have used "to new" packets, I have faced some perl installation issue.

6 apt-get update
7 apt-get install vim screen sudo lib32gmp3-dev libgmp3-dev sysstat libexpat1 libidn11 perl-modules wget lzma
8 cat debian.installzibbra.apt
9 echo "deb Index of /debian squeeze main
10 echo "deb Index of /debian squeeze main" > /etc/apt/sources.list
11 apt-get update
12 apt-get install libgmp3c2
13 perl -V
14 echo "deb Index of /debian testing main" > /etc/apt/sources.list
15 apt-get update
19 echo " mxtest.mydomain.com" >> /etc/hosts
20 cat /etc/apt/sources.list
21 vi /etc/apt/sources.list
22 apt-get -t testing install libc6-dev
23 vi /etc/apt/sources.list
24 ls
25 tar -xzvf zcs-8.0.5_GA_5839.UBUNTU12_64.20130910124038.tgz
26 poweroff
27 history
28 ls
29 cd zcs-8.0.5_GA_5839.UBUNTU12_64.20130910124038
30 ls
31 ls -lah
32 vi /etc/apt/sources.list
33 apt-get update
34 ls
35 apt-get romove exim-light-deamon exim
36 apt-get remove exim-light-deamon exim
37 apt-get remove exim-light-deamon
38 cat ../debian.installzibbra.history
39 apt-get remove exim4-daemon-light exim4
40 cat ../debian.installzibbra.history
41 ./install.sh --platform-override

That's more-or-less all
It shows that it was possible, but some packet-dependency issue are tricky at this moment.

I still have this virtual machine, so it You have some question, feel free to ask.