From libHaru.org wiki

Mailing lists

General development and support mailing list: libharu@googlegroups.com

Web archive: http://groups.google.com/group/libharu

Official language: English

You can subscribe to the list without creating a Google account by sending an empty email to libharu-subscribe@googlegroups.com (and unsubscribe using libharu-unsubscribe@googlegroups.com).

Please keep in mind that the list is premoderated and it might take some time for your messages to get there (all new users and their messages are checked manually).