/usr/lib/libsylpheed-plugin-0.so.1 is in sylpheed 3.2.0~beta5-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libsylpheed-plugin-0.so.1.1.0
/usr/lib/libsylpheed-plugin-0.so.1.1.0