net-mail/dovecot-2.2.9 links against app-arch/xz-utils (liblzma.so) though there is no such dependency declared in the ebuild. Please add $( use_with lzma ) to configure and lzma use-flag with corresponding xz-utils dependency. Reproducible: Always
While at it, please also add dependencies on app-arch/bzip2 and sys-lib/libz. Those may be part of @system (as are xz-utils) but as their use is connected to use-flags putting them explicitly in dependencies is helpful. net-mail/dovecot-2.2.10 is affected as well as net-mail/dovecot-2.2.9.
Thanks for the report. Should be fixed in dovecot-2.2.12.