Updating kernel is not an option, I'm getting the following message when trying to run iptables
root@mail:/etc/postfix# iptables -L
libkmod: ERROR ../libkmod/libkmod.c:554 kmod_search_moddep: could not open moddep file '/lib/modules/2.6.32-5-xen-amd64/modules.dep.bin'
iptables v1.4.14: can't initialize iptables table `filter': Table does not exist (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
UPDATE:
after running
root@mail:/home/admin# sudo depmod
I get
ERROR: could not open directory /lib/modules/2.6.32-5-xen-amd64: No such file or directory
FATAL: could not search modules: No such file or directory
and after
root@mail:/home/admin# sudo modinfo ip_tables
I get
libkmod: ERROR ../libkmod/libkmod.c:554 kmod_search_moddep: could not open moddep file '/lib/modules/2.6.32-5-xen-amd64/modules.dep.bin'
ERROR: Module alias ip_tables not found.
It looks like kernel update is a must.