Basic mailserver configuration on RHEL10

Quick and dirty (10 minutes) very basic configuration of mailserver with postfix, dovecot and mysql/mariadb.
It is the update of the previous basic_mailserver_configuration_on_RHEL_derivates

Prerequisites

configure your DNS properly

• A record matching the FQDN of this server
• MX record for the domains to the IP of this server
• ensure reverse IP is configured properly or some external servers can refuse your email
• not mandatory: SPF record for your domains matching with the IP of your server

SSL certificates

dnf install epel-release
dnf install certbot

Create cert with your FQDN server name (server08.vettore.org in the example)

certbot certonly -d server08.vettore.org

install Mariadb and set up tables

timedatectl set-timezone Europe/Rome
dnf install mariadb
dnf install mariadb-server
systemctl enable mariadb --now

Enter mariadb console and:

create database mailserver;
use mailserver;

USERS

CREATE TABLE `users` (
 `email` varchar(200) NOT NULL,
 `enabled` int(11) DEFAULT 1,
 `password` varchar(128) NOT NULL,
 `imap_enabled` int(11) DEFAULT 1,
 `smtp_enabled` int(11) NOT NULL DEFAULT 1,
 `smtp_username` varchar(45) DEFAULT NULL,
 PRIMARY KEY (`email`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8

There are more fields than in usual tutorials you can retrieve online.

• enabled: user can receive emails
• imap_enabled: user can retieve email with IMAPs protocol
• smtp_enabled: user can use smtp service to send email from a remote client
• smtp_username: to authenticate SMTP, can be different from the email address

DOMAINS

CREATE TABLE
`domains` ( `domain` varchar(200) NOT NULL,
`enabled` int(11) NOT NULL DEFAULT '1', PRIMARY KEY (`domain`))
 ENGINE=MyISAM DEFAULT CHARSET=utf8 

ALIASES

CREATE TABLE `aliases` ( `email` varchar(128) NOT NULL,
`alias` varchar(255) NOT NULL,
`enabled` int(11) DEFAULT '1',
 PRIMARY KEY (`email`)) ENGINE=MyISAM DEFAULT CHARSET=utf8;

ADD a test user (enter in mariadb console):

insert into users set email='paperino@274512.xyz', password='segretina412', smtp_username='paperino';
insert into domains set domain='274512.xyz';

Grant privileges:

grant select on mailserver.* to postfix@localhost identified by 'yoursecretpassword'

Postfix

dnf install postfix postfix-mysql
groupadd -g150 vmail
useradd -r  -u150 -d /var/vmail -s /sbin/nologin -g vmail vmail
mkdir /var/vmail
chown vmail:vmail /var/vmail

Edit /etc/postfix/main.cf and change/add the following line accordingly (replace paths of your cerificates)

inet_protocols = all
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-users.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-aliases.cf
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1

smtpd_tls_cert_file = /etc/letsencrypt/live/server08.vettore.org/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/server08.vettore.org/privkey.pem
smtpd_tls_security_level = may
smtp_tls_CApath = /etc/letsencrypt/live/server08.vettore.org
smtp_tls_CAfile = /etc/letsencrypt/live/server08.vettore.org/chain.pem

smtpd_client_restrictions = permit_mynetworks,
       permit_sasl_authenticated,
       reject_unauth_destination,
       reject_unknown_sender_domain,
       reject_unknown_reverse_client_hostname,
       reject_rbl_client b.barracudacentral.org,
       reject_rbl_client blackholes.easynet.nl,
       reject_rbl_client proxies.blackholes.wirehub.net,
       reject_rbl_client bl.spamcop.net,
 
#disabled for several reasons (be careful to enable again)

#       reject_rbl_client sbl.spamhaus.org,
#        reject_rbl_client zen.spamhaus.org,
#        reject_rhsbl_sender blackhole.securitysage.com,
#        reject_rbl_client cbl.abuseat.org,

Setup the connectors configured above (virtual_xxx)

/etc/postfix/mysql-virtual-domains.cf:

user = postfix
password = yuorsecretpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT 1 FROM domains WHERE domain='%s' AND enabled=1

/etc/postfix/mysql-virtual-users.cf :

user = postfix
password = yoursecretpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT 1 FROM users where email='%s'AND enabled=1

/etc/postfix/mysql-virtual-aliases.cf

user = postfix
password = yoursecretpassword
hosts = 127.0.0.1
dbname = mailserver
query = SELECT alias FROM aliases WHERE email='%s' AND enabled=1

You can check your configuration with postmap (1 returned in case of success)

postmap q 274512.xyz mysql:/etc/postfix/mysql-virtual-domains.cf
postmap -q paperino@274512.xyz mysql:/etc/postfix/mysql-virtual-users.cf

Add this to your /etc/postfix/master.cf

dovecot unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/libexec/dovecot/deliver -f ${sender} -d ${recipient}

Enable & start service

systemctl enable postfix --now

Dovecot IMAP

dnf install dovecot dovecot-mysql

edit conf.d/10-mail.conf and add/uncomment this

mail_location = maildir:/var/vmail/%d/%n/Maildir

edit /etc/dovecot/conf.d/auth-sql.conf.ext

comment out the first userdb section

remove comment from the last userdb section end edit as follows:

userdb {
 driver = static
 args = uid=150 gid=150 home=/var/vmail/%d/%n allow_all_users=yes
}

Rename the above file removing .ext extension

Verify path in the passdb section of the above file. Should be /etc/dovecot/dovecot-sql.conf.ext
You must create this file:

driver=mysql
default_pass_scheme = PLAIN
connect= host=127.0.0.1 port=3306 dbname=mailserver user=postfix password=yoursecretpassword
password_query = SELECT password, email as user  FROM users where email='%u' AND imap_enabled=1

in conf.d/10-ssl.conf add the certifcate and key replacing with the path of the certificate created above

ssl_cert = </etc/letsencrypt/live/server08.vettore.org/fullchain.pem
ssl_key = </etc/letsencrypt/live/server08.vettore.org/privkey.pem
#leave the following commented for normal configuration
#ssl_ca = </etc/letsencrypt/live/server08.vettore.org/chain.pem

in dovecot.conf remove comment from protocol. Remove pop3 if not needed. Remove submission if you wish to configure SMTP auth with a different service (see cirus-sasl section below)

protocols = imap lmtp

Add to the bottom:

mail_uid=vmail
mail_gid=vmail

first_valid_uid = 150
last_valid_uid = 150

service stats {
 unix_listener stats-reader {
   group = vmail
   mode = 0666
 }
  unix_listener stats-writer {
    group = vmail
    mode = 0666
  }
}

Disable PAM auth (otherwise you will get errors in /var/log/secure.
Comment out the following in /etc/dovecot/conf.d/10-auth.conf

#!include auth-system.conf.ext

Start end enable service

systemctl enable dovecot --now

SMTP auth with cyrus-sasl

Not the easiest way: you can use directly dovecot to authenticate SMTP users.
But the advantage of cyrus-sasl is you can configure different users for SMTP and IMAP or enable/disable SMTP for IMAP users. The table structure created above have fields for this purpose.

Setting smtp_enabled=0 means the users cannot use SMTP auth (cannot send email from outside using this server as relay)

dnf install cyrus-sasl cyrus-sasl-plain cyrus-sasl-lib cyrus-sasl-sql

edit /etc/sasl2/smtpd.conf

pwcheck_method: auxprop
mech_list: PLAIN LOGIN
auxprop_plugin: sql
sql_usessl: no
sql_engine: mysql
sql_hostnames: localhost
sql_user: postfix
sql_database: mailserver
sql_passwd: yoursecretpassword
sql_select: select password from users where username = '%u' AND smtp_enabled=1
log_level: 3

uncomment the following line in /etc/postfix/masters.cf

submission inet n       -       n       -       -       smtpd

add the following to /etc/postfix/main.cf

smtpd_use_tls = yes
smtpd_sasl_path = smtpd
smtpd_sasl_auth_enable = yes
smtpd_sasl_type = cyrus
smtpd_sasl_security_options = noanonymous
smtpd_tls_auth_only = yes

restart services and start (anable) saslauthd

systemctl restart postfix
systemctl restart dovecot
systemctl enable saslauthd --now

Verify SSL connections

SMTP starttls

openssl s_client -starttls smtp -servername server08.vettore.org -connect server08.vettore.org:587

IMAP startls

openssl s_client -starttls imap -servername server08.vettore.org -connect server08.vettore.org:143