Dovecot 虚拟用户登录失败（权限被拒绝，我们不在 5000 组中）

Question

我有：

• Ubuntu 17.04
• Dovecot 2.2.27 (c0f36b0)
• Postfix 3.1.4
• 普通 unix 用户的邮件位于 /home/bob/Maildir
• 虚拟用户的邮件位于 /var/mail/vhosts/domain.com/bob/Maildir

普通用户可以正常接收邮件。虚拟用户尝试登录时失败。日志显示如下错误：

2017-09-14 22:44:55 auth: Error:
passwd-file(travler at travler.net,54.210.254.169,<EYwzYDFZWoY20v6p>):
stat(/var/mail/vhosts/travler.net/shadow) failed: Permission denied
(euid=114(dovecot) egid=121(dovecot) missing +x perm: /var/mail/vhosts,
we're not in group 5000(vmail), dir owned by 5000:5000 mode=0750)

之前有一位用户在 2015 年遇到过类似的问题： https://dovecot.org/list/dovecot/2015-July/101469.html

建议他看看https://wiki2.dovecot.org/UserIds… 没有得到更具体的建议。我查看了页面。我尝试添加mail_uid 和mail_gid。没有成功。

就我而言，我看到的是：

# sudo -u dovecot groups
dovecot vmail

# sudo -u dovecot cat /var/mail/vhosts/travler.net/shadow
<file contents>

我有一个 vmail 用户：

# id vmail
uid=5000(vmail) gid=5000(vmail) groups=5000(vmail)

# ls -la /var/mail/vhosts
total 0
drwxr-s--- 1 vmail vmail 246 Jun 30 11:23 .
drwxrwsrwt 1 mail  mail   26 Dec  5  2016 ..
drwxr-s--- 1 vmail vmail  66 Sep 14 23:11 travler.net

# ls -l /var/mail/vhosts/travler.net/
total 8
-rw-r----- 1 vmail vmail 174 Dec  5  2016 passwd
-rw-r----- 1 vmail vmail 173 Dec  5  2016 shadow
drwxr-s--- 1 vmail vmail 450 Sep  9 13:16 travis.belmont
drwxr-s--- 1 vmail vmail 750 Sep 13 14:14 travler

我已经设置了 mail_gid 和 mail_uid

# doveconf  -n|grep id
mail_gid = 5000
mail_uid = 5000

密码文件有以下几行：

travler::5000:5000::/var/mail/vhosts/travler.net/travler::userdb_mail=maildir:~

这是我的完整配置：

# doveconf -n
# 2.2.27 (c0f36b0): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.16 (fed8554)
# OS: Linux 4.10.0-33-generic x86_64 Ubuntu 17.04 btrfs
log_path = /var/log/dovecot
log_timestamp = "%Y-%m-%d %H:%M:%S "
mail_gid = 5000
mail_location = maildir:/home/%u/Maildir
mail_privileged_group = mail
mail_uid = 5000
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
}
passdb {
  args = username_format=%n /var/mail/vhosts/%d/shadow
  driver = passwd-file
}
plugin {
  sieve = file:~/sieve;active=~/.dovecot.sieve
}
protocols = " imap"
service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0666
  }
}
service imap-login {
  inet_listener imap {
    port = 0
  }
}
ssl_cert = [snip]
ssl_cipher_list = [snip]
ssl_dh_parameters_length = 2048
ssl_key =  # hidden, use -P to show it
ssl_protocols = !SSLv3 !SSLv2
userdb {
  driver = passwd
}
userdb {
  args = username_format=%n /var/mail/vhosts/%d/passwd
  driver = passwd-file
}

我需要设置什么才能让 dovecot 作为 vmail 运行/修复此错误？