It seems that there is a problem with the button "show_compose_message" in the "Messaging" menu
This button is never show. There are two conditions to be showed: [widget.action.params.view_inbox and widget.action.params.show_compose_message]
It seems that widget.action.params.show_compose_message is always false.
See in mail_thread_view.xml :
field name="params" eval=""{ 'domain': [ ('to_read', '=', True), ('starred', '=', False), ], 'view_mailbox': True, 'view_inbox': True, 'read_action': 'read', 'show_compose_message': False }""/>
This modification has been added into the commit #8637.1.1 by Martin Trugaux Maybe it's not a bug but then could it be possible to have more information about this change?