I have not run RoundCube under mod_security, but from what I know
about mod_security, I am sure it can be done.
mod_security simply applies a [long] list of rules to the contents of
each request (GET/POST/HEAD/etc) including the header.
Depending on your ruleset, you often have to add exceptions for
certain applications, and/or disable entire rules server-wide. What
I've done in the past is: tail -F error_log while you use the
application. Then you add exceptions for the uri (e.g. "/roundcube")
or hostname or disable certain rules inside the modsecurity*.conf
files.
Thank you for your interest in my problem
how easy to apply new rules to mod_security ?