Dovecot 不听 993(imaps)

我只为 imap 服务器打开了端口 993（imap），但 dovecot 打开了端口 143。我在 dovecot -n 中的 dovecost 设置如下

sudo dovecot -n
# 2.2.18: /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.8 (0c4ae064f307+)
# OS: Linux 4.2.0-24-generic x86_64 Ubuntu 15.10
auth_mechanisms = plain login
mail_location = maildir:~/Maildir
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}
passdb {
  driver = pam
}
protocols = " imap"
service auth {
  unix_listener /var/spool/postfix/private/auth {
    group = postfix
    mode = 0666
    user = postfix
  }
}
service imap-login {
  inet_listener imaps {
    port = 993
    ssl = yes
  }
}
ssl = no
userdb {
  driver = passwd
}

但是 netstat 只表示打开了 143 端口

sudo netstat -ntpl
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      15556/master
tcp        0      0 0.0.0.0:139             0.0.0.0:*               LISTEN      1922/smbd
tcp        0      0 0.0.0.0:5900            0.0.0.0:*               LISTEN      1156/x11vnc
tcp        0      0 0.0.0.0:143             0.0.0.0:*               LISTEN      16566/dovecot
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      1381/dnsmasq
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      746/sshd
tcp        0      0 127.0.0.1:631           0.0.0.0:*               LISTEN      660/cupsd
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      15556/master
tcp        0      0 0.0.0.0:445             0.0.0.0:*               LISTEN      1922/smbd
tcp6       0      0 :::3306                 :::*                    LISTEN      1134/mysqld
tcp6       0      0 :::587                  :::*                    LISTEN      15556/master
tcp6       0      0 :::139                  :::*                    LISTEN      1922/smbd
tcp6       0      0 :::5900                 :::*                    LISTEN      1156/x11vnc
tcp6       0      0 :::143                  :::*                    LISTEN      16566/dovecot
tcp6       0      0 :::80                   :::*                    LISTEN      1809/apache2
tcp6       0      0 :::22                   :::*                    LISTEN      746/sshd
tcp6       0      0 ::1:631                 :::*                    LISTEN      660/cupsd
tcp6       0      0 :::25                   :::*                    LISTEN      15556/master
tcp6       0      0 :::443                  :::*                    LISTEN      1809/apache2
tcp6       0      0 :::445                  :::*                    LISTEN      1922/smbd

实际上，我也不使用 iptable 和 ufw 。

有没有人知道这件事并帮助解决这个问题？这是昨天从 ubuntu 15.04 升级到 15.10 发生的。