The legacy code in this distribution is covered by a simple license from CMU.
All new code in this distribution is covered by the GNU LGPL, version 2.1.

New portions of code are copyrighted by the libSieve author and maintainer,
Aaron Stone, and contributions are assumed to have thier copyrights assigned
to the libSieve author unless specifically stated and agreed to otherwise.

As of verison 2.1.4 (formerly 2.2.0_pre1) of libSieve, all code previously
held under a larger, "advertising," license from CMU has been removed or
replaced. As the new code is covered by the LGPL, the entire distribution
therefore fall under the LGPL. See section 2.b. of the GNU General Public
License for terms.

The LGPL prohibits proprietary distribution and derivation of libSieve,
but does not restrict its use by proprietary programs. You are welcome
and encouraged to use libSieve for proprietary projects, but must provide
libSieve to end users with the same rights and privileges.

This is the simple CMU license:
/***********************************************************
        Copyright 1998 by Carnegie Mellon University

                      All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the name of Carnegie Mellon
University not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior
permission.

CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE FOR
ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
******************************************************************/