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Description

Postfix is a SMTP (Simple Mail Transfer Protocol) server.

Ports

port	description
587 incoming	standard port for email submission by mail clients. StartTLS protocol.
465 incoming	SMTP with TLS encryption (deprecated)
25 incoming	mandatory port to receive emails from other SMTP servers
25 outgoing	mandatory port to send emails to other SMTP servers

Commands

# vérifier la configuration
sudo postfix check

# recharger la configuration
sudo postfix reload

# affiche les paramètres actuels de Postfix
postconf -pf

# affiche les paramètres par défaut
postconf -df

Basic Configuration

/etc/postfix/main.cf

mydomain = domain.net
# mydomain = localdomain (localdomain is replaced during installation)

myhostname = mail.domain.net
# myhostname = <hostname>.localdomain

# domain name to use in outbound mail, ex: user@myorigin
# send mail as user@$mydomain
myorigin = $mydomain
# myorigin = $myhostname

# domains to receive mail for
# add $mydomain
mydestination = $myhostname localhost.$mydomain localhost $mydomain
# mydestination = $myhostname, localhost.$mydomain, localhost

alias_maps = hash:/etc/aliases
# alias_maps = hash:/etc/aliases, nis:mail.aliases

# forward mail from the local machine only
mynetworks_style = host
# mynetworks_style = ${{$compatibility_level} < {2} ? {subnet} : {host}}
# compatibility_level = 0

# relay_domains = ${{$compatibility_level} < {2} ? {$mydestination} : {}}
# never forward mail from strangers
relay_domains = 

# delivery method: direct or indirect (another smtp server)
relayhost = [smtp.internet-provider.fr]
# relayhost =   (direct delivery to Internet)

hostname

Not sure that it is needed if localhost is used.

# current hostname
hostnamectl status

sudo hostnamectl set-hostname mail.domain.fr

/etc/hosts

127.0.0.1    localhost mail.domain.fr
::1          localhost ip6-localhost ip6-loopback mail.domain.fr

# re-login to see the changes then run
hostname -f

TLS encryption for outgoing mail

/etc/postfix/main.cf

smtp_use_tls = yes
smtp_tls_security_level = encrypt
smtp_tls_note_starttls_offer = yes
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

SMTP2GO

La box d’Orange bloque le port 25 en sortie ipv4 pour limiter l’envoi de spam.
L'envoie d'email doit donc se faire via un relais smtp.

create an account on SMTP2GO
go to your domain registrar (OVH) to add DNS entry
create an SMTP account on SMTP2GO and use it in the following config files

/etc/postfix/main.cf

# TLS encryption outgoing mail
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl/smtp2go.conf
smtp_sasl_security_options = noanonymous
header_size_limit = 4096000
relayhost = [mail.smtp2go.com]:2525
relay_destination_concurrency_limit = 20

/etc/postfix/sasl/smtp2go.conf

[mail.smtp2go.com]:2525 USER:PASSWORD

# create the db
sudo postmap hash:/etc/postfix/sasl/smtp2go.conf
sudo chmod 600 /etc/postfix/sasl/smtp2go.conf     # root:root 600
sudo chmod 600 /etc/postfix/sasl/smtp2go.conf.db  # root:root 600

Orange

Orange n’autorise plus l'envoie d'email provenant d'un autre domaine via son relais smtp.

La box d’Orange bloque le port 25 en sortie ipv4 pour limiter l’envoi de spam.
L'envoie d'email doit donc se faire via le smtp d'orange.

/etc/postfix/main.cf

relayhost = [smtp.orange.fr]:587
smtp_sasl_password_maps = hash:/etc/postfix/sasl/orange.conf
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
# smtp_sasl_security_options = noplaintext, noanonymous

#broken_sasl_auth_clients = yes
#smtpd_sasl_local_domain = $myhostname

/etc/postfix/sasl/orange.conf

[smtp.orange.fr]:587 compte@orange.fr:password

# générer la db
sudo postmap hash:/etc/postfix/sasl/orange.conf
sudo chmod 600 /etc/postfix/sasl/orange.conf     # root:root 600
sudo chmod 600 /etc/postfix/sasl/orange.conf.db  # root:root 600

TLS encryption for incoming mail

/etc/postfix/main.cf

smtpd_tls_security_level = may
smtpd_tls_key_file = /etc/letsencrypt/live/domain.net/privkey.pem
smtpd_tls_cert_file = /etc/letsencrypt/live/domain.net/fullchain.pem

smtpd_tls_received_header = yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache

# log level (default 0)
smtpd_tls_loglevel = 1
# 0 → no log
# 1 → Log on TLS handshake completion
# 2 → Also log levels during TLS negotiation
# 3 and 4. Use log level 3 only in case of problems. Use of log level 4 is strongly discouraged.

Improve security

/etc/postfix/main.cf

# restriction for the others SMTP servers who deliver emails to postfix
smtpd_client_restrictions = reject_unknown_client_hostname reject_unauth_pipelining
smtpd_helo_restrictions = reject_invalid_helo_hostname reject_non_fqdn_helo_hostname reject_unknown_helo_hostname
smtpd_sender_restrictions = reject_non_fqdn_sender

# servers that are not using helo are not properly configured or sending spam
smtpd_helo_required = yes
# allow to log recipient address information when the connected client breaks any of the reject rules
smtpd_delay_reject = yes

# disable VRFY (verify), allows brute force attack on user accounts
disable_vrfy_command = yes

SMTP Authentication using SASL client with Dovecot

Postfix supports the Dovecot SASL (Simple Authentication and Security Layer) implementation.
Dovecot is a POP/IMAP (Post Office Protocol / Interactive Message Access Protocol) server, it has its own configuration to authenticate POP/IMAP clients.
Communication between the Postfix SMTP server and Dovecot SASL happens over a UNIX-domain socket.

/etc/postfix/main.cf

smtpd_sasl_type = dovecot
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions = permit_sasl_authenticated, permit_mynetworks, reject_unauth_destination
smtpd_sasl_path = private/auth

Allow incoming port 587 (submission)

By default Postfix listen incoming STMP client connections from port 25.
In addition you may allow the port 587 to receive incoming connections from SMTP client to send emails.
StartTLS protocol is used: communications start in plain text and if possible, upgrades to TLS.

/etc/postfix/master.cf

submission inet n       -       y       -       -       smtpd
  -o syslog_name=postfix/submission
  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_tls_auth_only=yes
  -o smtpd_reject_unlisted_recipient=no
  -o smtpd_client_restrictions=$mua_client_restrictions
  -o smtpd_helo_restrictions=$mua_helo_restrictions
  -o smtpd_sender_restrictions=$mua_sender_restrictions
  -o smtpd_recipient_restrictions=
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

/etc/postfix/main.cf

mua_client_restrictions = permit_sasl_authenticated reject
# on BlueMail Android app, Helo command rejected, need fully-qualified hostname
# mua_helo_restrictions = reject_non_fqdn_helo_hostname reject_invalid_helo_hostname reject_unknown_helo_hostname
mua_helo_restrictions = reject_invalid_helo_hostname
mua_sender_restrictions = reject_non_fqdn_sender

Allow incoming port 465 (SMTPS)

By default Postfix listen incoming STMP client connections from port 25.
In addition you may allow the port 465 to receive incoming connections from SMTP client to send emails.
Implicit TLS protocol is used: communications start encrypted with TLS.

/etc/postfix/master.cf

smtps     inet  n       -       y       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_reject_unlisted_recipient=no
  -o smtpd_client_restrictions=$mua_client_restrictions
  -o smtpd_helo_restrictions=$mua_helo_restrictions
  -o smtpd_sender_restrictions=$mua_sender_restrictions
  -o smtpd_recipient_restrictions=
  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
  -o milter_macro_daemon_name=ORIGINATING

DKIM

apt install opendkim opendkim-tools

/etc/opendkim.conf

Domain        domain.fr
KeyFile       /etc/dkimkeys/dkim.key
# selectors are used to permit multiple keys under the same organization's domain name
Selector      mail
# prevent trivial reformatting in header and body destroying trust
Canonicalization    relaxed/simple
# if postfix is running in chroot
Socket    local:/var/spool/postfix/var/run/opendkim/opendkim.sock

/etc/default/opendkim

# to use a Unix socket with postfix in a chroot:
RUNDIR=/var/spool/postfix/var/run/opendkim

# generate the key
opendkim-genkey -r -s mail -b 2048 -d domain.fr
# DNS record containing the public key: mail.txt
# private key: mail.private

# copy the key
sudo mv mail.private /etc/dkimkeys/dkim.key
# check the owner of the file (root:root 600)

# configuration des droits d'accès
# add postfix in the opendkim group
sudo adduser postfix opendkim
# if postfix is running in chroot
sudo mkdir -p /var/spool/postfix/var/run/opendkim
sudo chown opendkim:opendkim /var/spool/postfix/var/run/opendkim

mail._domainkey.domain.fr. IN TXT "v=DKIM1; h=sha256; k=rsa; s=email; p=xxx";
# mail: selector
# domain.fr: domain
# v: version
# h: hash / algorithme
# k: type de clé
# s: type de service
# p: clé publique base64

/etc/postfix/main.cf

# if postfix is running in chroot, there is no / before var
non_smtpd_milters = unix:var/run/opendkim/opendkim.sock
smtpd_milters = unix:var/run/opendkim/opendkim.sock

Aliases

/etc/aliases

postmaster: <user>
root:       <user>

# run after modification of the file /etc/aliases
sudo newaliases

Transport Map & Relayhost Map

/etc/postfix/main.cf

transport_maps = hash:/etc/postfix/transport

emails sent to your own domain are delivered locally
email sent to gmail.com are delivered normally by performing MX lookup
all other emails are delivered via the relay host

/etc/postfix/transport

your-domain.com       local 
gmail.com             smtp
*                     relay:[smtp-relay.sendinblue.com]:587

# build the index file
sudo postmap /etc/postfix/transport

Test

telnet localhost 25
ehlo localhost
# vérifier que les lignes suivantes sont bien affichées
# 250-STARTTLS
# 250-AUTH
mail from: root@domain.fr
rcpt to: user@gmail.com
data
subject: test
test
.
quit

openssl s_client -connect localhost:25 -starttls smtp
openssl s_client -connect localhost:587 -starttls smtp
openssl s_client -connect localhost:465 -starttls smtp

Log

journalctl
/var/log/mail.log
/var/log/mail.err

/etc/postfix/main.cf

# TLS logging outgoing
smtp_tls_loglevel = 1
# TLS logging incoming
smtpd_tls_loglevel = 1

Debug

Mailboxes

By default Postifx will use mbox for the mailbox format.

/etc/postfix/main.cf

# use maildir and store emails in the /home/<user>/maildir directory
home_mailbox = maildir/

UFW

# allow incoming SMTP (25) to receive emails from other SMTP servers
sudo ufw allow Postfix

# allow incoming SMTP (587) to receive emails from SMTP client over StartTLS
sudo ufw allow "Postfix Submission"

# allow incoming SMTPs (465) to receive emails from SMTP client over TLS
sudo ufw allow "Postfix SMTPS"

Fail2ban

/etc/fail2ban/jail.d/enabled.local

[postfix]
enabled = true

[postfix-rbl]
enabled = true

Installation

apt install postfix
# General type or mail configuration: Internet site
# System mail name: domain.fr

Erreurs

Our system has detected that 550-5.7.1 this message does not meet IPv6 sending guidelines

Our system has detected that 550-5.7.1 this message does not meet IPv6 sending guidelines regarding PTR 550-5.7.1 records and authentication.
Please review 550-5.7.1 https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 .

/etc/postfix/main.cf

inet_protocols = ipv4

Postfix et ubuntu

Sommaire

Liens

Description

Ports

Commands

Basic Configuration

hostname

TLS encryption for outgoing mail

SMTP2GO

Orange

TLS encryption for incoming mail

Improve security

SMTP Authentication using SASL client with Dovecot

Allow incoming port 587 (submission)

Allow incoming port 465 (SMTPS)

DKIM

Aliases

Transport Map & Relayhost Map

Test

Log

Debug

Mailboxes

UFW

Fail2ban

Installation

Erreurs

Our system has detected that 550-5.7.1 this message does not meet IPv6 sending guidelines

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