vi /etc/postfix/main.cf

SSL/TLS证书，这个证书，最好是免费一年的！自己去申请就好，推荐用腾讯云的免费证书

SMTP  SSL/TLS

 code
### SSL/TLS Settings
smtp_tls_security_level = may
smtpd_tls_cert_file = /etc/letsencrypt/live/mail.testdom.com/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/mail.testdom.com/privkey.pem
smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache
smtpd_tls_session_cache_timeout = 3600s
smtpd_tls_received_header = yes
smtpd_tls_loglevel = 1

vi /etc/postfix/master.cf

smtps inet n - n - - smtpd                               取消注解
-o smtpd_tls_wrappermode=yes                             取消注解
-o smtpd_sasl_auth_enable=yes                            取消注解
-o smtpd_recipient_restrictions=permit_sasl_authenticated,reject  取消注解

完了

postconf -n
postfix check
systemctl restart postfix
systemctl status postfix

. dovecot設定

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

ssl_cert = </etc/你证书的位置
ssl_key = </etc/你证书的位置

10-master.conf 设置

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

service imap-login {
inet_listener imap {
port = 0     用不到了
}
inet_listener imaps {
port = 993   取消注释

ssl = yes   取消注释

}

service pop3-login {
inet_listener pop3 {
port = 0     用不到了
}
inet_listener pop3s {
port = 995     取消注释
ssl = yes     取消注释
}
}


完了

doveconf -n
systemctl restart dovecot
systemctl status dovecot