Old versions of Odoo did not correctly manage message_id of mail messages.
Thread formation was based on information present in References and/or in
In-Reply-To of replies to emails. Message-Ids could contain model and
res_id of a record. Thread formation was done using this information.
However commit 8253453d64 fixed that behavior
by correctly checking in existing mail_messages to find matching message-ids.
Message found was set as parent and thread formation was correctly done without
collision or possible issues with badly formatted Message-Ids.
A compatibility mode was introduced at the same time to handle previous versions
of Odoo. This commit removes this compatibility as it was done long enough
to ensure compatibility is not required anymore.
[TESTS] mail: tests updated, compat mode should raise in all cases now
Thibault Delavallée
323dab7653