无法对authdeamon套接字进行身份验证

Question

尝试在我的Gmail帐户中添加SMTP服务器时收到错误消息。添加POP3很好，但谷歌在尝试添加SMTP时返回此错误：

435 Unable to authenticate at present code(435)

我的邮件服务器在日志文件中给出了这个响应：

# tail -f /var/log/exim/main.log

2014-08-13 14:00:41 plain authenticator failed for (mail-ig0-f171.google.com) [209.85.213.171]: 435 Unable to authenticate at present (set_id=123testmail@domain.com): failed to connect to socket /var/spool/authdaemon/socket: Permission denied

默认情况下，套接字的权限如下：

# ls -al /var/spool/authdaemon/socket
srwxrwxrwx. 1 root root 0 Aug 13 00:38 /var/spool/authdaemon/socket

在收到电子邮件时，我在Exim的日志文件中收到此错误：

2014-08-13 14:38:19 1XHZGR-0005Il-LD == 123testmail@domain.com R=vdomain T=vmail defer (13): Permission denied: failed to open tmp/1407940699.H500223P20471.mail.domain.com (10 tries)

服务器在CentOS 6上使用Courier-imap

运行