I noticed that ISPconfig comes with redis, but not the newest version. I wanna know why is ISPconfig using redis, and if there is any issue if I remove redis.
Are you sure redis came with ISPC and not some other package you installed yourself? As far as I know redis doesn't come with ISPC. There is no reason to.
Redis does not come with ISPConfig; it's a package of your Linux distribution. But the ISPConfig auto-installer installs Redis as Redis is used by rspamd, which is the spamfilter used on recent. So if you would uninstall redis, your mail system will stop working.
I guess it comes down to how you define 'comes with' So yes, it comes with ISPConfig if you define it broadly as a package getting installed by the auto-installer, but it's not part of ISPConfig itself or a package we provide.
I look at it like most will do. Clean install >> Install ISPC >> System has redis installed Conclusion: ISPC installed redis
