Install Postfix + Dovecot e-mail server

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Note

Postfix is a mail transfer agent (MTA) responsible for sending out and receiving emails between servers.

Dovecot is a mail delivery agent (MDA) responsible for sending out and receiving emails between a server and its users.

Mail-stack-delivery is a combined package containing both Postfix and Dovecot. It would be easier than to install Postfix and Dovecot separately.

Re-direct to server ports​

Set the internet router to re-direct the following connections to server ports:

  • SMTP = port 25 (for receiving or sending emails)
  • secure SMTP = port 465 (for receiving or sending emails securely)
  • IMAP = port 143 (for retrieiving emails)
  • secure IMAP = port 993 (for retrieving emails securely)
  • POP3 = port 110 (for retrieving emails)

Install both Postfix and Dovecot​

Install the combined package:

$ sudo apt-get install mail-stack-delivery

Reconfigure Postfix

Reconfig:

$ sudo dpkg-reconfigure postfix

Use Tab key to change selection.

Select "Internet Site".

Enter the following information:

System mail name: <fully qualified domain name, such as "kctang.com.hk">
Root and postmaster mail recipient: <such as "kctang">
Other destinations to accept mail: <fully qualified domain name, such as "kctang.com.hk">, <server name such as "server1">, localhost.localdomain, localhost
Force synchronous updates on mail queue: No
Local networks: 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
Use procmail for local delivery: No
Mailbox size limit (bytes): 0
Local address extension character: +
Internet protocols to use: all

Activate the changes:

$ sudo systemctl reload postfix
or
$ sudo service postfix reload

Edit "main.cf" settings:

$ gksudo gedit /etc/postfix/main.cf

Specify:

myhostname = kctang.com.hk
# last line changed from server name to fully qualified domain name,
# otherwise some servers would not accept e-mails sent without fully qualified domain name, 2/4/2014
message_size_limit = 204800000
# last line added to increase the default 10 times, 5/4/2014
# increased to 20 times, 20/9/2018
maximal_queue_lifetime = 0
# last line added to report unsuccessful delivery immediately instead of after the default of 5 days, 12/4/2018
body_checks = regexp: /etc/postfix/body_checks
# last line added to refer to another file to check contents of email bodies, 29/9/2018

Edit "master.cf" settings:

$ gksudo gedit /etc/postfix/master.cf

Specify​:

smtp      inet  n       -       y       -       -       smtpd
smtps     inet  n       -       y       -       -       smtpd
# last line uncommented
   -o smtpd_sasl_auth_enable=yes
# last line added to enable STARTTLS authentication
   -o smtpd_client_restrictions=permit_sasl_authenticated,reject
# last line added to reject if not authenticated, no space after ","
   -o smtpd_tls_wrappermode=yes
# last line added to force use of TLS
   -o milter_macro_daemon_name=ORIGINATING
# last line added

Create "body_checks" file:

$ gksudo gedit /etc/postfix/body_checks

Specify​ one or more lines of texts within //:

/unique text contained in email you do not want to receive/ DISCARD

"DISCARD" means delete from the server.

Change Dovecot settings

Edit config file:

$ gksudo gedit /etc/dovecot/conf.d/99-mail-stack-delivery.conf

Specify:

mail_location = maildir:~/Maildir:LAYOUT=fs
# LAYOUT=fs added to last line, to use "/" instead of "." to denote sub-folders
# IMAP configuration
protocol imap {
    mail_max_userip_connections = 1000
    # 10 in last line increased to 1000
    imap_client_workarounds = delay-newmail
}
# POP3 configuration
protocol pop3 {
    mail_max_userip_connections = 50
    # 10 in last line increased to 50
    pop3_client_workarounds = outlook-no-nuls oe-ns-eoh
}

Activate the changes:

$ sudo systmctl reload postfix
or
$ sudo service postfix reload
and
$ sudo systemctl restart dovecot
or
$ sudo service dovecot reload

Verify success

See whether the postfix server is running:

$ telnet localhost 25

should display:

220 kctang.com.hk ESMTP Postfix (Ubuntu)

ehlo localhost

should display the following:

250-kctang.com.hk

250-PIPELINING

250-SIZE 102400000

250-VRFY

250-ETRN

250-STARTTLS

250-ENHANCEDSTATUSCODES

250-8BITMIME

250 DSN

Ctrl-]

to exit to "telnet >" prompt.

quit

to exit telnet.

Try also:

$ telnet localhost 995

similarly:

$ telnet localhost 465

should display either one:

Connected to localhost

Connected to kctang.com.hk

"Ctrl-]"

 to exit to "telnet >" prompt.

quit

to exit telnet.

Specify mail forwarding

Edit "aliases" file:

$ sudo gedit /etc/aliases

Specify​:

postmaster: kctang
kctcl: kctcl, kctclpop

meaning:

  • forwarding e-mails sent to postmaster to kctang, no email will be left at postmaster
  • forwarding e-mails sent to kctcl to kctcl (itself) and to kctclpop, i.e. making a copy

Activate setting:

$ sudo newaliases

Revisions

29/9/2018: Add "body_checks" for spam control.

20/9/2018: Increase message_size_limit to 20 times the default.

5/4/2018: Increase message_size_limit to 10 times the default.

12/4/2014:  Specify maximal_queue_lifetime to notify unsuccessful delivery immediately.

2/4/2014: Specify fully qualified domain name.

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