Description of problem:
version 2.xx miss feature that was in version 1.xx

Version-Release number of selected component (if applicable):
dovecot-2.0.*

How reproducible:

not possible make operation as was possible in version 1:
connect to dovecot service on IP1 - dovecot must serve users that related to domain1 located in database1
connect to dovecot service on IP2 - dovecot must serve users that related to domain2 located in database2
login must be with username that form not as user@domain but simple user

...

existing version 1 config file:
------------------------
server mail.domain1.tld {
protocols = imaps pop3s
ssl_cert_file = /etc/pki/cert1.pem
ssl_key_file = /etc/pki/cert1.key
listen = 123.123.123.1
ssl_listen = 123.123.123.1
default_mail_env = mbox:/tmp:INBOX=/var/mail/domain1.tld/%n:INDEX=MEMORY
  pop3_uidl_format = %08Xu%08Xv
auth default {
  mechanisms = plain

  passdb ldap {
    args= /etc/dovecot-ldap.conf.domain1.tld1
  }
  userdb ldap {
    args= /etc/dovecot-ldap.conf.domain1.tld1
  }
}
login_process_per_connection = yes
login_max_processes_count = 4
login_processes_count = 1
}
server mail.domain2.tld {
protocols = imaps pop3s
ssl_cert_file = /etc/pki/cert2.pem
ssl_key_file = /etc/pki/cert2.key
listen = 123.123.123.2
ssl_listen = 123.123.123.2
default_mail_env = mbox:/tmp:INBOX=/var/mail/domain2.tld/%n:INDEX=MEMORY
  pop3_uidl_format = %08Xu%08Xv
auth default {
  mechanisms = plain

  passdb ldap {
    args= /etc/dovecot-ldap.conf.domain2.tld2
  }
  userdb ldap {
    args= /etc/dovecot-ldap.conf.domain2.tld2
  }
}
login_process_per_connection = yes
login_max_processes_count = 4
login_processes_count = 1
}
------------------------
/etc/dovecot-ldap.conf.domain1.tld and /etc/dovecot-ldap.conf.domain2.tld refers to different ldap databases

Actual results:
-

Expected results:
version 2 must have that functionality that was in version 1