Historical information:

• We moved to the Forum on May 2017. Prior to that we used to offer a User mailing list and a Nabble Forum working on top of this mailing list (it's been decommissioned). There was also a Gmane archive (also decommissioned). We've decided to move to a Discourse-based forum for a nicer and simpler user experience (for example even though users were registered on Nabble, they were still required to also register on the user mailing list before being able to post on the list from Nabble).
• On 18th of September 2019 we also moved the development mailng list to the Forum.
• You can search for old messages using Markmail.

The last 2 are private mailing lists for reading

• Anyone can write to these lists to report issues (no subscription needed)
• But unlike public mailing list above, these mailing lists are only accessible for core committers and some other trusted persons. Unregistered users can not read archives of this mailing list, because it might contain sensitive security details.
• If you want to contribute to discussions on these lists, start contributing and ask for permission by posting on the xwiki.org forum (in the Other category) and explain why you need access. Committers will decide whether you will get access or not.