Log Message:
Update to Dovecot 2.1.10

+ imap: Implemented THREAD=ORDEREDSUBJECT extension.
+ Added "doveadm exec" command to easily execute commands from libexec_dir,
  e.g. "doveadm exec imap -u user@domain"
+ Added "doveadm copy" command.
+ doveadm copy/move: Added optional user parameter to specify the source
  username. This allows easily copying mails between different users.
+ Added namespace { disabled } setting to quickly enable/disable namespaces.
  This is especially useful when its value is returned by userdb.
+ Added mailbox_alias plugin. It allows creating mailbox aliases using
  symlinks.
+ imapc storage: Added imapc_max_idle_time setting to force activity on
  connection.
+ fts-solr: Expunging multiple messages is now faster.
- director: In some conditions director may have disconnected from another
  director (without logging about it), thinking it was sending invalid data.
- imap: Various fixes to listing mailboxes.
- pop3-migration plugin: Avoid disconnection from POP3 server due to idling.
- login processes crashed if there were a lot of local {} or remote {} settings
  blocks.