As per https://gitlab.gnome.org/GNOME/gspell/-/issues/15 the owner/maintainer agreed to close the gspell mailing list. Could you please create a gspell platform tag (they should post in platform, right?). I know the tags are global btw, trying to give clear instructions to the existing subscribers.
You can open a topic anywhere, really; some people might want to limit the notifications on a tag to a specific category, if that tag is widely used—e.g. using the “Community” category for the “announcement” tag to only get project announcements and avoid application release announcements.