Mail Server : SSL/TLS Setting2020/11/12

	Configure SSL/TLS to encrypt connections.
[1]	Get SSL certificate, Refer to here.
[2]	Configure Postfix and Dovecot.

[root@mail ~]#

vi /etc/postfix/main.cf

# line 709, 715: comment out

smtpd_tls_cert_file = /etc/pki/tls/certs/postfix.pem

smtpd_tls_key_file = /etc/pki/tls/private/postfix.key

# add to the end (replace certificate to your own one)

smtpd_use_tls = yes
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
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 17,18,20: uncomment

submission inet n       -       n       -       -       smtpd
  -o syslog_name=postfix/submission
#  -o smtpd_tls_security_level=encrypt
  -o smtpd_sasl_auth_enable=yes

# line 29-32: uncomment

smtps     inet  n       -       n       -       -       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 8: change (if set SSL required, specify [required])

ssl =

yes

# line 14,15: specify certificates

ssl_cert = <

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

ssl_key = <

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

[root@mail ~]#

systemctl restart postfix dovecot

[3]	If SELinux is enabled, restote context for certificates.

[root@mail ~]#

restorecon -v /etc/letsencrypt/live/mail.srv.world/fullchain.pem

[root@mail ~]#

restorecon -v /etc/letsencrypt/live/mail.srv.world/privkey.pem

[4]	If Firewalld is running, allow SMTP-Submission/SMTPS/POP3S/IMAPS services. SMTP-Submission uses [587/TCP] (used STARTTLS), SMTPS uses [465/TCP], POP3S uses [995/TCP], IMAPS uses [993/TCP].

[root@mail ~]#

firewall-cmd --add-service={smtp-submission,smtps,pop3s,imaps} --permanent

success
[root@mail ~]#

firewall-cmd --reload

success

[5]	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. (this example shows to select [STARTTLS])

[6]	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, this example shows to select [STARTTLS])

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

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