Pigeonhole 0.4.16 cannot work with dovecot2 releases older than
2.2.26. Up the registered dependency to force dovecot2 at least
2.2.26.0 (the latest version).

See also: http://www.dovecot.org/list/dovecot-news/2016-November/000331.html

PR: 213978
Submitted by: maintainer (Larry Rosenman)