The file etc/MAILINGLISTS describes the purpose of each GNU mailing list (see Informational files for Emacs). For those lists which are gatewayed with newsgroups, it lists both the newsgroup name and the mailing list address. The Emacs mailing lists are also described at the Emacs Savannah page.
The newsgroup news:comp.emacs is for discussion of Emacs programs in general. The newsgroup news:gnu.emacs.help is specifically for GNU Emacs. It therefore makes no sense to cross-post to both groups, since only one can be appropriate to any question.
Messages advocating “non-free” software are considered unacceptable on
any of the
gnu.* newsgroups except for news:gnu.misc.discuss,
which was created to hold the extensive flame-wars on the subject.
“Non-free” software includes any software for which the end user can't
freely modify the source code and exchange enhancements. Be careful to
gnu.* groups from the ‘Newsgroups:’ line when
posting a followup that recommends such software.
news:gnu.emacs.bug is a place where bug reports appear, but avoid posting bug reports to this newsgroup directly (see Reporting bugs).