Dear, in the past we used the roundcube plugin, in order to let the mail user to manage their email account directly from the webmail. But for simplicity, right now we prefer to let the email account to access directly to the ispconfig control panel (with the email credentials) in order to manage only the mailbox from there). But, from this access, the mail user can't add/remove whitelist/blacklist. It's there a way to allow them to do that? Because we don't want return back to the webmail plugin if it's possible. Thank you.
No. Such a feature is not implemented right now. You can of course create a feature request in the bug tracking system https://git.ispconfig.org/ispconfig/ispconfig3