I know that dovecot has configuration options to make LookOut! work:
# Workarounds for various client bugs:
# Never send EXISTS/RECENT when replying to FETCH command. Outlook
# seems to think they are FETCH replies and gives user "Message no
# in server" error. Note that OE6 still breaks even with this
# if synchronization is set to "Headers Only".
# Outlook and Outlook Express never abort IDLE command, so if no mail
# arrives in half a hour, Dovecot closes the connection. This is
# fine, except Outlook doesn't connect back so you don't see if
You might need to do some googling.