Log Message:
Update to 2.3.16. From the changelog:

* Any unexpected exit() will now result in a core dump. This can
  especially help notice problems when a Lua script causes exit(0).
* auth-worker process is now restarted when the number of auth
  requests reaches service auth-worker { service_count }. The default
  is still unlimited.
+ Event improvements: Added data_stack_grow event and http-client
  category. See https://doc.dovecot.org/admin_manual/list_of_events/
+ oauth2: Support RFC 7628 openid-configuration element. This allows
  clients to support OAUTH2 for any server, not just a few hardcoded
  servers like they do now. See openid_configuration_url setting in
  dovecot-oauth2.conf.ext.
+ mysql: Single statements are no longer enclosed with BEGIN/COMMIT.
+ dovecot-sysreport --core supports multiple core files now and does
  not require specifying the binary path.
+ imapc: When imap_acl plugin is loaded and imapc_features=acl is used,
  IMAP ACL commands are proxied to the remote server. See
  https://doc.dovecot.org/configuration_manual/mail_location/imapc/
+ dict-sql now supports the "UPSERT" syntax for SQLite and PostgreSQL.
+ imap: If IMAP client disconnects during a COPY command, the copying
  is aborted, and changes are reverted. This may help to avoid many
  email duplicates if client disconnects during COPY and retries it
  after reconnecting.
- master process was using 100% CPU if service attempted to create more
  processes due to process_min_avail, but process_limit was already
  reached. v2.3.15 regression.
- Using attachment detection flags wrongly logged unnecessary "Failed
  to add attachment keywords" errors. v2.3.13 regression.
- IMAP QRESYNC: Expunging UID 1 mail resulted in broken VANISHED
  response, which could have confused IMAP clients. v2.3.13 regression.
- imap: STORE didn't send untagged replies for \Seen changes for
  (shared) mailboxes using INDEXPVT. v2.3.10 regression.
- rawlog_dir setting would not log input that was pipelined after
  authentication command.
- Fixed potential infinite looping with autoexpunging.
- Log event exporter: Truncate long fields to 1000 bytes
- LAYOUT=index: ACL inheritance didn't work when creating mailboxes
- Event filters: Unquoted '?' wildcard caused a crash at startup
- fs-metawrap: Fix to handling zero sized files
- imap-hibernate: Fixed potential crash at deinit.
- acl: dovecot-acl-list files were written for acl_ignore_namespaces
- program-client (used by Sieve extprograms, director_flush_socket)
  may have missed status response from UNIX and network sockets,
  resulting in unexpected failures.