Yahoo! Inc. claims patent rights concerning DomainKeys and DKIM.
Details of the claim can be found at
<https://datatracker.ietf.org/ipr/920/>. Their licensing statement
from that page reads as follows, as of 2019-09-16:

"Yahoo! licenses its Necessary Patent Claims contained in the patents and
patent applications disclosed above under either of two separate license
agreements, one of which is the DomainKeys Patent License Agreement (v1.2), and
the other is the GNU General Public License v2.0 (and no other version)."

It is believed that this will cause normal users no legal problems, but the
packager can't guarantee anything.

For more information about DKIM, see http://www.dkim.org

 -- Magnus Holmgren <holmgren@debian.org>, Mon, 16 Sep 2019 21:59:29 +0200