在装有 Debian 10 (buster) 的 Digital Ocean droplet 中，尝试设置 postfix + dovecot 电子邮件服务器。尝试执行以下操作postfix start：
$ sudo postfix start
postfix/postfix-script: warning: symlink leaves directory: /etc/postfix/./makedefs.out
postfix/postfix-script: starting the Postfix mail system
postfix/postfix-script: fatal: mail system startup failed
地位：
$ sudo postfix status
postfix/postfix-script: the Postfix mail system is not running
重新加载：
$ sudo postfix reload
postfix/postfix-script: fatal: the Postfix mail system is not running
权限：
$ sudo postfix set-permissions
重新开始：
$ sudo systemctl status postfix
● postfix.service - Postfix Mail Transport Agent
Loaded: loaded (/lib/systemd/system/postfix.service; enabled; vendor preset: enabled)
Active: active (exited) since Wed 2020-04-15 02:36:43 UTC; 19s ago
Process: 7465 ExecStart=/bin/true (code=exited, status=0/SUCCESS)
Main PID: 7465 (code=exited, status=0/SUCCESS)
abr 15 02:36:43 mail systemd[1]: Starting Postfix Mail Transport Agent...
abr 15 02:36:43 mail systemd[1]: Started Postfix Mail Transport Agent.
重试：
$ sudo postfix start
postfix/postfix-script: warning: symlink leaves directory: /etc/postfix/./makedefs.out
postfix/postfix-script: starting the Postfix mail system
postfix/postfix-script: fatal: mail system startup failed