I'm pretty sure that our ISPCONFIG servers use AMAVIS-NEW and SPAMASSASSIN to operate. So I believe that this plugin: http://squirrelmail.org/plugin_view.php?id=224 would work best. Could someone confirm if this is the case? or if there is something better to use?
yes, thats right. The last update of this plugin has been 11 years ago, so not sure if it will still work. But I never used it so I cant give you any details on that.