Cyrus-imap-2.12 с autocreate patch. Патч обязательно!
/usr/local/etc/imapd.conf
configdirectory: /var/imap
partition-default: /var/spool/imap
unixhierarchysep: yes
altnamespace: yes
sieveusehomedir: false
sievedir: /var/imap/sieve
autocreatequota: 30000000
autocreateinboxfolders: Send|Drafts|Spam|trash
createonpost: true
virtdomains: on/usr/local/etc/saslauthd.conf
ldap_servers: ldap://192.168.1.1
ldap_bind_dn: CN=userfree,CN=Users,DC=sample,DC=org
ldap_bind_pw: 123456
ldap_version: 3
ldap_search_base: DC=sample,DC=org
#ldap_filter: (sAMAccountName=%u)
ldap_filter: (mail=%u@%r)
#ldap_filter: (mail=%u)
ldap_debug: -1
Авторизация cyrus-imap происходит через saslauthd. Тот в свою очередь через ldap с AD.