Mail Server : Install Postfix2025/09/23

	Install Postfix to configure SMTP Server. SMTP uses [25/TCP].
[1]	This example shows to configure SMTP-Auth to use Dovecot's SASL function.

root@mail:~#

apt -y install postfix sasl2-bin

# on this example, proceed to select [No Configuration]
# because configure all manually

+------+ Postfix Configuration +-------+
| General type of mail configuration:  |
|                                      |
|       No configuration               |
|       Internet Site                  |
|       Internet with smarthost        |
|       Satellite system               |
|       Local only                     |
|                                      |
|                                      |
|       <Ok>           <Cancel>        |
|                                      |
+--------------------------------------+

root@mail:~#

cp /usr/share/postfix/main.cf.dist /etc/postfix/main.cf

root@mail:~#

vi /etc/postfix/main.cf

# line 82 : uncomment
mail_owner = postfix

# line 97 : if listen only IPv4, change to [ipv4]
inet_protocols = all

# line 107 : uncomment and specify hostname
myhostname = mail.srv.world

# line 114 : uncomment and specify domainname
mydomain = srv.world

# line 133 : change
myorigin = $mydomain

# line 149 : uncomment
inet_interfaces = all

# line 197 : uncomment
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain

# line 285 : uncomment
mynetworks_style = subnet

# line 299 : add your local network
mynetworks = 127.0.0.0/8, 10.0.0.0/24

# line 423 : uncomment
alias_maps = hash:/etc/aliases

# line 434 : uncomment
alias_database = hash:/etc/aliases

# line 456 : uncomment
home_mailbox = Maildir/

# line 592 : comment out and add
#smtpd_banner = $myhostname ESMTP $mail_name (Debian)
smtpd_banner = $myhostname ESMTP

# line 665 : uncomment
sendmail_path = /usr/sbin/sendmail

# line 670 : uncomment
newaliases_path = /usr/bin/newaliases

# line 675 : uncomment
mailq_path = /usr/bin/mailq

# line 681 : uncomment
setgid_group = postdrop

# add follows to last line
# disable SMTP VRFY command
disable_vrfy_command = yes

# require HELO command to sender hosts
smtpd_helo_required = yes

# limit an email size
# example below means 10M bytes limit
message_size_limit = 10240000

# SMTP-Auth settings
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_auth_enable = yes
smtpd_sasl_security_options = noanonymous
smtpd_sasl_local_domain = $myhostname
smtpd_recipient_restrictions = 
  permit_mynetworks,
  permit_sasl_authenticated,
  reject_unauth_destination

root@mail:~#

touch /etc/aliases

root@mail:~#

newaliases

root@mail:~#

systemctl restart postfix

[2]

Configure additional settings for Postfix if you need.
It's possible to reject many spam emails with the settings below.

However, you should consider to apply the settings,
because sometimes normal emails are also rejected with them.
Especially, there are SMTP servers that forward lookup and reverse lookup of their hostnames on DNS do not match even if they are not spammers.

root@mail:~#

vi /etc/postfix/main.cf

# add to last line
# reject unknown clients that forward lookup and reverse lookup of their hostnames on DNS do not match
smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname, permit

# rejects senders that domain name set in FROM are not registered in DNS or 
# not registered with FQDN
smtpd_sender_restrictions = permit_mynetworks, reject_unknown_sender_domain, reject_non_fqdn_sender

# reject hosts that domain name set in FROM are not registered in DNS or 
# not registered with FQDN when your SMTP server receives HELO command
smtpd_helo_restrictions = permit_mynetworks, reject_unknown_hostname, reject_non_fqdn_hostname, reject_invalid_hostname, permit

root@mail:~#

systemctl reload postfix

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