q37-mail-aliases-and-postfix

Énoncé§

Solve this question on: app-srv1

1. Install Postfix as a local-only MTA listening on 127.0.0.1.
2. Redirect mail addressed to root and webmaster to the local user alice.
3. Create a mailing-list alias devs that forwards to alice, bob, and an external [email protected].
4. Send a test mail to root and verify it arrives in alice’s mailbox; write the output of mailq into /opt/course/37/queue.

Solution§

Install§

Debian (choose Local only in the dialog):

sudo DEBIAN_FRONTEND=noninteractive apt install -y postfix mailutils

RHEL:

sudo dnf install postfix mailx
sudo alternatives --set mta /usr/sbin/sendmail.postfix
sudo systemctl enable --now postfix

Main config: /etc/postfix/main.cf. Service map: /etc/postfix/master.cf.

Step 1 — Local-only listening§

In /etc/postfix/main.cf:

myhostname    = app-srv1.lfcs.lan
mydomain      = lfcs.lan
myorigin      = $mydomain
inet_interfaces = loopback-only
inet_protocols  = ipv4
mydestination = $myhostname, localhost.$mydomain, localhost
mynetworks    = 127.0.0.0/8

sudo postfix check
sudo systemctl restart postfix
ss -tlnp | grep :25

Step 2+3 — Aliases§

Edit /etc/aliases:

# basic redirections
postmaster: root
root:       alice
webmaster:  alice

# mailing list
devs:       alice, bob, [email protected]

Rebuild the hashed database (mandatory after every edit):

sudo newaliases
# or:
sudo postalias /etc/aliases

Step 4 — Send a test mail and inspect§

echo "test body" | mail -s "test subject" root
mailq > /opt/course/37/queue                  # mail queue
sudo postqueue -p                              # equivalent
sudo postqueue -f                              # flush queue (retry now)
sudo postsuper -d ALL                          # delete all queued msgs

Check delivery:

sudo su - alice
mail                                           # interactive client
# or just read the mbox:
cat /var/mail/alice

Postfix logs go to syslog / journald:

sudo journalctl -u postfix -n 50
sudo tail -f /var/log/mail.log                 # Debian
sudo tail -f /var/log/maillog                  # RHEL

.forward per-user§

Each user can override delivery with ~/.forward:

# /home/alice/.forward
[email protected]
\alice           # also keep a local copy

Permissions must be reasonable (chmod 600 ~/.forward).

Virtual aliases (different domain hosting)§

Useful when receiving mail for multiple domains. In main.cf:

virtual_alias_domains = otherdomain.test
virtual_alias_maps   = hash:/etc/postfix/virtual

/etc/postfix/virtual:

[email protected]    alice
[email protected]      alice, bob
@otherdomain.test           catchall

Build the hash and reload:

sudo postmap /etc/postfix/virtual
sudo systemctl reload postfix

Useful diagnostics§

postconf -n                                    # non-default settings
postconf -d mail_version                       # defaults
postmap -q root hash:/etc/aliases.db
postfix check
sudo postfix reload

IMAP — Dovecot quickstart§

If the question asks for IMAP/IMAPS:

sudo apt install dovecot-imapd
# /etc/dovecot/dovecot.conf
protocols = imap
listen = *
mail_location = mbox:~/mail:INBOX=/var/mail/%u
# enable SSL via /etc/dovecot/conf.d/10-ssl.conf

Test:

openssl s_client -connect localhost:993 -crlf