The most important changes since v2.1.4:

* IMAP: When neither the session nor the mailbox has modseq tracking
enabled, return the mailbox as having NOMODSEQ in SELECT/EXAMINE
reply. Old versions in this situation always simply returned
HIGHESTMODSEQ as 1, which could have broken some clients.

+ dict file: Added optional fcntl/flock locking (default is dotlock)
+ fts-solr: doveadm fts rescan now resets indexes, which allows
reindexing mails. (This isn't a full rescan implementation like
fts-lucene has.)
+ doveadm expunge: Added -d parameter to delete mailbox if it's
empty after expunging.
- IMAP: Several fixes related to mailbox listing in some configs
- director: A lot of fixes and performance improvements
- v2.1.4 didn't work without a mail home directory set
- mbox: Deleting a mailbox didn't delete its index files.
- pop3c: TOP command was sent incorrectly
- trash plugin didn't work properly
- LMTP: Don't add a duplicate Return-Path: header when proxying.
- listescape: Don't unescape namespace prefixes.