Domain access (ping) from outside server and not from inside

hi,
I am on a VPS, have Virtualmin with some domains of my own.

For some time, I mentioned that internal processes cannot see their own domain. Let us take the domain yanfouom.net : you can reach it from anywhere by a ping, but not when I am connected in a terminal on the VPS ! I made a mistake somewhere.
Can you please help me ? Thanks per advance.
Here are some facts :

In a terminal on the server, you type :

x@vps296125:~$ ping yanfouom.net

you get:

PING yanfouom.net (51.255.197.10) 56(84) bytes of data.
^C
yanfouom.net ping statistics —
7 packets transmitted, 0 received, 100% packet loss, time 6047ms"

If I type the command :
>netstat -taupen | grep 53
I get :

tcp 0 0 0.0.0.0:465 0.0.0.0:* LISTEN 0 12537 -
tcp 0 0 51.255.197.10:53 0.0.0.0:* LISTEN 107 11070 -
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 107 11047 -
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 0 12531 -
tcp 0 0 127.0.0.1:953 0.0.0.0:* LISTEN 107 11320 -
tcp6 0 0 :::465 :::* LISTEN 0 12538 -
tcp6 0 0 :::53 :::* LISTEN 107 10998 -
tcp6 0 0 :::25 :::* LISTEN 0 12532 -
udp 0 0 51.255.197.10:53 0.0.0.0:* 107 11069 -
udp 0 0 127.0.0.1:53 0.0.0.0:* 107 11046 -
udp6 0 0 :::53 :::* 107 10997 -

Any clue / idea where to look ? Thks !

Assuming you are using iptables - have you “blocked” ICMP?

https://vitux.com/how-to-block-allow-ping-using-iptables-in-ubuntu/

thank you for your idea / suggestion, No I do not have such line in iptables. I tested without some lines. Fail2bain removed also is not the solution.
I tested the server in rescue mode (without the firewall mainly) and it works , but in “normal” mode it does not.
It shoud come from elsewhere.

I saw by iptable -L that I had a problem, I removed that line and all is correct - thanks to all !