Howard Chu @ Symas@dalias my favorite was always hosts whose IP address is encoded in their DNS name. I used to just flat reject them but now I only greylist them because more subscription mailers are using dynamic hosts for sending.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.