Maybe I am missing it but is there a way for an admin/moderator to see the IP address of the user in the conversation that was started and\or includes them?
SELECT ip_id, user_id, content_type,
content_id, action, log_date,
INET_NTOA(CONV(HEX(ip), 16, 10)) AS ip
FROM xf_ip
WHERE content_type = 'conversation_message'
AND content_id = 1
You would need to change the content_id from 1 to whatever the message ID of the message is that you want to know the IP for. You can find the message ID by hovering over the date the message was posted.