LAN Mail Server

1 Introduction

1.1 Aim

Setting an Internet Message Access Protocol (IMAP) server for a Local Area Network (LAN)

• Mail server: cyber8, a ThinkPad X230 set up with CentOS 8.1
• Mail client:   cyber7, another ThinkPad X230, set up with CentOS 7.8
• Mail software
  • Dovecot: IMAP server and Mail Delivery Agent (MDA)
  • Postfix: Mail Transfer Agent (MTA)
  • Thunderbird: email client / Mail User Agent (MUA)

1.2 Context

All hosts connected to ISP-provided Modem/Router

• DHCP-configured LAN 192.168.0.0/24
• Router IPv4 address: 192.168.0.1
• cyber7 IP addresses   (fixed by the Modem/Router)
  • IPv4: 192.168.0.210
  • IPv6: 2001:8003:22bc:1700:7787:2b17:cc6f:5b46
• cyber8 IP addresses   (fixed by the Modem/Router)
  • IPv4: 192.168.0.53
  • IPv6: 2001:8003:22bc:1700:66be:1375:b866:a57b
• Domain Name System (cf. the DNS page for the setup)
  • Server: cyber8
  • Domain Name: rshome.lan
• Host fully qualified names
  • cyber7.rshome.lan
  • cyber8.rshome.lan

2 Setup

2.1 Firewall

Open all machines' firewalls (server and clients) as follows

• Simple Mail Transfer Protocol (SMTP) and Secure variant
  • firewall-cmd --permanent --add-service smtp --add-service smtps
  • firewall-cmd --permanent --add-port=25/tcp --add-port=465/tcp --add-port=587/tcp
• Internet Message Access Protocol (IMAP) and Secure variant
  • firewall-cmd --permanent --add-service imap --add-service imaps
  • firewall-cmd --permanent --add-port=143/tcp --add-port=993/tcp
• Post Office Protocol (POP3) and Secure variant
  • firewall-cmd --permanent --add-service pop3 --add-service pop3s
  • firewall-cmd --permanent --add-port=110/tcp --add-port=995/tcp
• firewall-cmd --reload

2.2 cyber8 Mail Server

2.2.1 RPMs

• dnf install   dovecot   postfix

2.2.2 Dovecot

• Edit   /etc/pki/dovecot/dovecot-openssl.cnf   and update as follows
  • C=AU
  • ST=NSW
  • L=Sydney
  • CN=cyber8.rshome.lan

  (Note: the CN line indicating the mail server host is crucial for the mail system to work)

  • emailAddress=root@rshome.lan
• Run   /usr/libexec/dovecot/mkcert.sh   to generate the SSL certificate from above values

• Edit   /etc/dovecot/dovecot.conf   and update as follows
  • protocols = imap pop3 lmtp

  (do not try serving the protocol "submission" as its implementation in dovecot-2.3.8 is buggy and breaks the processing of other protocols)

  • listen = *, ::
• Edit   /etc/dovecot/conf.d/10-mail.conf   and update as follows
  • mail_location = mbox:~/mail:INBOX=/var/mail/%u
  • mail_access_groups = mail
  • first_valid_uid = ...

  (In case some users identifiers (uid) are below the default (1000))

• systemctl restart dovecot
• systemctl enable dovecot

2.2.3 Postfix

• Edit /etc/postfix/main.cf   and update as follows
  • myhostname = cyber8.rshome.lan
  • mydomain = rshome.lan
  • myorigin = $mydomain
  • inet_interfaces = all
  • mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
  • mynetworks = 192.168.0.0/16, 127.0.0.0/8, [2001:8003:22bc:1700::]/64, [::1]/128
  • mail_spool_directory = /var/spool/mail
• Append the following to /etc/aliases
  • root:   roger

  (emails sent to root redirected to Linux username roger)

  • roger.seguin:   roger

  (Declare roger.seguin@... as an alias to roger@...)

• Run the command   newaliases   to update the alias database
• systemctl restart postfix
• systemctl enable postfix

2.2.4 DNS

Add the instruction

IN   MX   0   cyber8.rshome.lan.

to the DNS Zone File   /var/named/named.rshome.lan

IN NS cyber8 cyber8 IN A 192.168.0.53 cyber8 IN AAAA 2001:8003:22bc:1700:66be:1375:b866:a57b cyber7 IN A 192.168.0.210 cyber7 IN AAAA 2001:8003:22bc:1700:7787:2b17:cc6f:5b46 IN MX 0 cyber8.rshome.lan.

2.3 cyber7 Mail Client

2.3.1 RPMs

• yum install   thunderbird   postfix

2.3.2 Email account

Launch Thunderbird

• Select Edit from the top bar, then Account Settings"

The "Account Settings" windows pops up

• Select Account Actions, then "Add Mail Account..."

  The "Set Up an Existing Email Account" window pops up

  • Your name:   Roger
  • Email address:   roger.seguin@rshome.lan
  • Password: ...

  (cyber8 login password)

  • Check Remember password
  • Press [Continue]

• A new "Set Up an Existing Email Account" window pops up
  • Change the incoming IMAP server to   cyber8.rshome.lan
  • Change the outgoing SMTP server to   cyber8.rshome.lan
  • Press [Re-test]

  The window should now display

  The following settings were found by probing the given server

  with all details updated accordingly

  • Press [Done]