[root@linux ~]# vi /etc/postfix/main.cf 

# 最終行に追加
smtpd_tls_cert_file = /etc/postfix/server.crt
smtpd_tls_key_file = /etc/postfix/server.key
smtpd_tls_session_cache_database = btree:/etc/postfix/smtpd_scache
smtpd_use_tls = yes

[root@linux ~]# vi /etc/postfix/master.cf 

#
# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (yes)   (never) (100)
# ==========================================================================
smtp      inet  n       -       n       -       -       smtpd
#submission inet  n      -       n       -       -       smtpd
#       -o smtpd_etrn_restrictions=reject
#       -o smtpd_client_restrictions=permit_sasl_authenticated,reject
# コメントを外す(有効にする)
smtps    inet  n       -       n       -       -       smtpd
  -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes
#submission inet  n      -       n       -       -       smtpd
#  -o smtpd_etrn_restrictions=reject
#  -o smtpd_enforce_tls=yes -o smtpd_sasl_auth_enable=yes
#628      inet  n       -       n       -       -       qmqpd
pickup    fifo  n       -       n       60      1       pickup
cleanup   unix  n       -       n       -       0       cleanup
qmgr      fifo  n       -       n       300     1       qmgr
#qmgr     fifo  n       -       n       300     1       oqmgr
# コメントを外す(有効にする)
tlsmgr    unix  -       -       n       1000?   1       tlsmgr
rewrite   unix  -       -       n       -       -       trivial-rewrite
bounce    unix  -       -       n       -       0       bounce

[root@linux ~]# ln -s /etc/httpd/conf/server.crt /etc/postfix/server.crt 
[root@linux ~]# ln -s /etc/httpd/conf/server.key /etc/postfix/server.key 

[root@linux ~]# ls -l /etc/postfix 
  :
lrwxrwxrwx 1 root root    26  7月  7 14:30 server.crt -> /etc/httpd/conf/server.crt
lrwxrwxrwx 1 root root    26  7月  7 14:30 server.key -> /etc/httpd/conf/server.key
  :

[root@linux ~]# vi /etc/dovecot.conf 

# Disable SSL/TLS support.
# コメントを外す(有効にする)
ssl_disable = no

# PEM encoded X.509 SSL/TLS certificate and private key. They're opened before
# dropping root privileges, so keep the key file unreadable by anyone but
# root. Included doc/mkcert.sh can be used to easily generate self-signed
# certificate, just make sure to update the domains in dovecot-openssl.cnf
#ssl_cert_file = /etc/pki/dovecot/certs/dovecot.pem
#ssl_key_file = /etc/pki/dovecot/private/dovecot.pem
# リンク済み証明書を指定する
ssl_cert_file = /etc/postfix/server.crt
# リンク済み秘密鍵を指定する
ssl_key_file = /etc/postfix/server.key

[root@linux ~]# service postfix restart 
Shutting down postfix:                                     [  OK  ]
Starting postfix:                                          [  OK  ]

[root@linux ~]# service dovecot restart 
Dovecot Imapを停止中:                                      [  OK  ]
Dovecot Imap を起動中:                                     [  OK  ]