Log Message:
Update to 0.5.16. From the changelog:

* .dovecot.sieve.log file now includes year in the header.
* Change Sieve script result execution to delay definitive action
  execution to the end of a successful Sieve script execution session.
  This is part of an effort to solve problems with the Sieve duplicate
  test. As a side-effect, some rare temporary-error cases yield
  different results, in which partial failure is more likely.