Where else can firewall rules hide?

Question

iptables

The task was to forward mail messages from the host machine to the container for further mail relaying to the admin.
In general, everything works except for postfixa access to the relay
ip host of the machine 192.168.1.50
ip lxc of the machine 192.168.1.35
Everything pings, you can even go from the container to the host via ssh and other ports - but the mail does not go and that's it!
iptables is disabled
ufw is also disabled

[email protected]:~# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
root@proxmox:~# ufw status
Status: inactive

But telnet stubbornly does not let from the host to the container....

[email protected]:~# telnet 192.168.1.35 25
Trying 192.168.1.35...
^C

Where else can there be rules?

Answer 1

Where else can there be rules?

Inside the virtual machine

[email protected]:~# telnet 192.168.1.35 25
Trying 192.168.1.35...
^C

And netstat -ltpndwhat does it say inside the virtual machine?

you can even go from the container to the host via ssh and other ports

In the examples, you are trying to enter the container from the host, but here you write about the opposite direction.
UPD : inside the iptables virtual machine, the author blocked everything except ssh/https/http