Mail Server : SSL/TLS Setting2026/06/08

	Configure SSL/TLS to use encrypted connections. SMTP-Submission uses [587/TCP] (used STARTTLS), SMTPS uses [465/TCP], POP3S uses [995/TCP], IMAPS uses [993/TCP].
[1]	Get SSL certificates, refer to here.
[2]	Configure Postfix and Dovecot.

root@mail:~#

vi /etc/postfix/main.cf

# add to last line

smtpd_tls_security_level = may
smtpd_tls_cert_file = /etc/letsencrypt/live/mail.srv.world/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/mail.srv.world/privkey.pem
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache

root@mail:~#

vi /etc/postfix/master.cf

# line 19, 20, 23 : uncomment

submission inet n       -       y       -       -       smtpd
  -o syslog_name=postfix/submission
#  -o smtpd_forbid_unauth_pipelining=no
#  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes

# add to last line if you like to enable smpts

smtps     inet  n       -       y       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
  -o smtpd_sasl_auth_enable=yes

root@mail:~#

vi /etc/dovecot/conf.d/10-ssl.conf

# line 6 : change

ssl =

yes

# line 18,20 : change to specify your certificates

ssl_server_cert_file =

/etc/letsencrypt/live/mail.srv.world/fullchain.pem

ssl_server_key_file =

/etc/letsencrypt/live/mail.srv.world/privkey.pem

root@mail:~#

systemctl restart postfix dovecot

[3]	If UFW is enabled, allow services. SMTP submissions (used with STARTTLS) use [587/TCP], SMTPS uses [465/TCP], POP3S uses [995/TCP], and IMAPS uses [993/TCP].

root@mail:~#

ufw allow submission

root@mail:~#

ufw allow submissions

root@mail:~#

ufw allow pop3s

root@mail:~#

ufw allow imaps

Rule added
Rule added (v6)

[4]	For Client's settings, ( Mozilla Thunderbird ) Open account's property and move to [Server Settings] on the left pane, then Select [STARTTLS] or [SSL/TLS] on [Connection security] field on the right pane.

[5]	Move to [Outgoing Server] on the left pane, then Select [STARTTLS] or [SSL/TLS] on [Connection security] field. Furthermore, change port to the used port. ([STARTTLS] uses [587], [SSL/TLS] uses 465.)

[6]	Verify possible to send or receive Emails normally.

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