Incorrect permissions set for new domains for email
When you generate a new domain in ISPConfig, and then start adding new mailboxes, you get some error messages when you try to login using SquirrelMail. Whilst all the files and subdirectories for 'domain.org.uk' are correct [user vmail], the top level domain in /var/mail/domain.org.uk is INCORRECTLY set to root:root permissions. Performing a chown -R vmail:vmail domain.org.uk correctly sets the permissions and email starts flowing correctly.
Apr 18 19:39:38 server1 dovecot: dovecot: Fatal: chdir(/var/vmail/domain.org.uk/treasurer/) failed: Permission denied (euid=5000(vmail) egid=5000(vmail) missing +x perm: /var/vmail/domain.org.uk)