With 18.1 and 18.2 I could call (via XMLRPC) message_post on a sale.order model (that had been previously sent to the customer via email) and it would post a message on the chatter that also reached the customer via email (the message in the chatter had the email icon).

With 18.3 it is no longer the case. The same API call only puts a note in the chatter, no email is sent.

I was relying on the old behavior. Is it somehow possible to achieve it with 18.3 ?