IP address leaked in email header?

Years ago, many webmail services (such as Hotmail and Yahoo Mail) used to include a X-Originating-Ip header in outgoing messages, which indicated IP address that the sender was using to connect to the webmail service to send the message. But, most of those services either encode this header now, or no longer include it. See https://en.wikipedia.org/wiki/X-Originating-IP for more info.