Mail server stopped delivering mails

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http://serverfault.com – It seems to me that I have broken some permission setting on my server what leads to the problem that the mail server does not work anymore. I use virtualmin/webmin, I have three domains pointing at the server with some subdomains. The mails cannot cannot be delivered for all domains. If I try to login to usermin via the webmail.domain.com url it loads forever after login. I have taken a look into the files: /var/log/mail.log and /var/log/mail.err what showed me the following error: dovecot: imap-login: Can't connect to auth server at default: Permission denied dovecot: pop3-login: Can't (HowTos)