Hi @phi,
Yes, this can be done by running a query from /admin/plugins/explorer once you have discourse-data-explorer plugin installed.
Here is the query you are looking for:
-- [params]
-- group_id :group
WITH user_groups AS (
SELECT gu.user_id
FROM groups g
JOIN group_users gu ON gu.group_id = g.id
WHERE g.id = :group
GROUP BY gu.user_id
)
SELECT u.email
FROM users u
INNER JOIN user_groups ug ON u.id = ug.user_id
WHERE u.id > 0
ORDER BY u.id DESC
The group name will be entered in group field, and once you run the query you will have the option to export the result, which will only contain user emails from the group you specified.
I hope this helps.