IMAP/ Getting all headers on command BODY[HEADER]

Hi,
I’m using an external software that connects to Bluemind (v5) via IMAP and I would needs to retrieves the complete list of header for a message when the imap command “FETCH UID BODY[HEADER]” is given.

The issue is that currently, only “standard headers” are returned (from to subject etc …) but not the other headers

Is there an option regarding the IMAP server configuration that could changes this behavior ?

Thank you in advance for your help