0. 환경 

sendmail 8.15.2

dovecot 2.2.36

let's encrypt 인증서 사용

1.  /etc/mail/sendmail.cf 수정

CACertPath=/etc/letsencrypt/live/mail.yeonghoon.kim
CACertFile=/etc/letsencrypt/live/mail.yeonghoon.kim/chain.pem
ServerCertFile=/etc/letsencrypt/live/mail.yeonghoon.kim/cert.pem
ServerKeyFile=/etc/letsencrypt/live/mail.yeonghoon.kim/privkey.pem

2. /etc/dovecot/conf.d/10-ssl.conf 수정

ssl = yes
ssl_cert = </etc/letsencrypt/live/mail.yeonghoon.kim/cert.pem
ssl_key = </etc/letsencrypt/live/mail.yeonghoon.kim/privkey.pem
ssl_ca = </etc/letsencrypt/live/mail.yeonghoon.kim/chain.pem

3. 데몬 재구동

systemctl restart sendmail.service

systemctl restart dovecot.service