# Serveur mail Postfix (désactiver les lignes des addresses IPV6)
#Adresse IP : 192.168.0.16
sudo nano /etc/hosts :
127.0.0.1       localhost
192.168.0.16    mail.univ-poitiers.fr mail
192.168.0.17    dns.univ-poitiers.fr dns

# Serveur DNS ((désactiver les lignes des addresses IPV6)
#Adresse IP : 192.168.0.17
sudo nano /etc/hostshosts
127.0.0.1       localhost
192.168.0.17    dns-bind.univ-poitiers.fr
192.168.0.16    mail.univ-poitiers.fr mail

Configuration supplémentaire :
$TTL    604800
@       IN      SOA     dns.univ-poitiers.fr. root.univ-poitiers.fr. (
                          2         ; Serial
                     604800         ; Refresh
                      86400         ; Retry
                    2419200         ; Expire
                     604800 )       ; Negative Cache TTL
;
@       IN      NS      dns.univ-poitiers.fr.
@       IN      MX      10 mail.univ-poitiers.fr.
@       IN      A       192.168.0.17
dns-bind     IN      A       192.168.0.17
mail    IN      A       192.168.0.16

Vérifications:
ubuntu@dns:~$ dig @192.168.0.17 univ-poitiers.fr MX

; <<>> DiG 9.18.30-0ubuntu0.22.04.2-Ubuntu <<>> @192.168.0.17 univ-poitiers.fr MX
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56455
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: 176ce8136a9364bc0100000067d2f7831bf7cb3daeb71f91 (good)
;; QUESTION SECTION:
;univ-poitiers.fr.		IN	MX

;; ANSWER SECTION:
univ-poitiers.fr.	604800	IN	MX	10 mail.univ-poitiers.fr.

;; ADDITIONAL SECTION:
mail.univ-poitiers.fr.	604800	IN	A	192.168.0.16

;; Query time: 1 msec
;; SERVER: 192.168.0.17#53(192.168.0.17) (UDP)
;; WHEN: Thu Mar 13 16:19:31 CET 2025
;; MSG SIZE  rcvd: 110


ubuntu@dns:~$ dig @192.168.0.17 mail.univ-poitiers.fr A

; <<>> DiG 9.18.30-0ubuntu0.22.04.2-Ubuntu <<>> @192.168.0.17 mail.univ-poitiers.fr A
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61681
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: e84831a573997dcf0100000067d2f7d47bd4cb5f50669d40 (good)
;; QUESTION SECTION:
;mail.univ-poitiers.fr.		IN	A

;; ANSWER SECTION:
mail.univ-poitiers.fr.	604800	IN	A	192.168.0.16

;; Query time: 1 msec
;; SERVER: 192.168.0.17#53(192.168.0.17) (UDP)
;; WHEN: Thu Mar 13 16:20:52 CET 2025
;; MSG SIZE  rcvd: 94

Vérification et correction du fichier hosts du serveur mail postfix: 

127.0.0.1       localhost
127.0.1.1       mail
192.168.0.16    mail.univ-poitiers.fr mail
192.168.0.17    dns.univ-poitiers.fr dns

Vérification et correction du fichier hosts du serveur DNS
127.0.0.1       localhost
127.0.1.1       dns
192.168.0.17    dns.univ-poitiers.fr dns
192.168.0.16    mail.univ-poitiers.fr mail

Vérifie la configuration de Postfix  /etc/postfix/main.cf: 
myhostname = mail.univ-poitiers.fr
mydomain = univ-poitiers.fr
myorigin = $mydomain

Vérification des log : sudo tail -f /var/log/mail.log
Pas de fichier mail.log