Debian 9 Stretch
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SSL Settings
2017/06/26
 
Configure SSL settings to encrypt datas in connection. SMTPS uses 465/TCP, POP3S uses 995/TCP, IMAPS uses 993/TCP.
[1]
Create certificates first, see here.
[2] Configure Postfix and Dovecot for SSL.
root@mail:~#
vi /etc/postfix/main.cf
# add follows to the end

smtpd_use_tls = yes
smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
smtpd_tls_cert_file = /etc/ssl/private/server.crt
smtpd_tls_key_file = /etc/ssl/private/server.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
root@mail:~#
vi /etc/postfix/master.cf
# line 28-30: uncomment

smtps     inet  n       -       -       -       -       smtpd
  -o syslog_name=postfix/smtps
  -o smtpd_tls_wrappermode=yes
root@mail:~#
vi /etc/dovecot/conf.d/10-ssl.conf
# line 6: change

ssl =
yes
# line 12,13: uncomment and specify certificate

ssl_cert = <
/etc/ssl/private/server.crt

ssl_key = <
/etc/ssl/private/server.key
root@mail:~#
systemctl restart postfix dovecot

[3] For Client's settings, ( Mozilla Thunderbird )
Open account's property and move to [Server Settings] on the left pane, then Select [SSL/TLS] on [Connection security] field on the right pane.
[4] Move to [Outgoing Server] on the left pane, then Select [SSL/TLS] on [Connection security] field. Furthermore, change port to [465] like follows.
[5] If your own self-signed certificates, the warning like follows are displayed, but it's no ploblem to proceed. Then it's possible to send or receive emails through SSL/TLS connection.
 
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