The preferred way for users to get in touch with the ARTS developers and other users is via the arts-users mailing list.
Note that you are not obliged to register. You are welcome to send your question directly to arts_users.mi (at) lists.uni-hamburg.de
Searchable archive on mail-archive.com

If you would like to participate in ARTS development, join the arts-dev mailing list.
Searchable archive on mail-archive.com

There is also a low volume announcement mailing list arts-announce mailing list.

Information on mailing lists for atmlab, qpack and typhon can be found on the tools page.