This is not supported on kqueue based systems currently, such as FreeBSD.

Dovecot supports moving connections that have issued IDLE to a special holding process, called imap-hibernate. This process is responsible for holding the idle processes until they need to be thawed.


imap_hibernate_timeout specifies the delay before moving users to imap-hibernate process. This requires inter-process communication between imap and imap-hibernate process.

imap_hibernate_timeout = 5s

service imap {
  # Note that this change will allow any process running as
  # $default_internal_user (dovecot) to access mails as any other user.
  # This may be insecure in some installations, which is why this isn't
  # done by default.
  unix_listener imap-master {
    user = $default_internal_user

# The following is the default already in v2.3.1+:
service imap {
  extra_groups = $default_internal_group
service imap-hibernate {
  unix_listener imap-hibernate {
    mode = 0660
    group = $default_internal_group

How it works

When client issues IDLE, the connection socket is moved to the hibernation process. This process is responsible for keeping all connections that are idling, until they issue some command that requires them to be thawed into a imap process. This way, memory and CPU resources are saved, since there is only one hibernation process.