I have a Debian Server with IMAP/Fetchmail/Postfix emails and other services already working and running. I am wondering if installing Zimbra would mess all my services and emails. I would like to install all packages but still like to be able to keep working the old way too, is that possible? Does Zimbra install its services to replace the ones I already have (read IMAP, mail directories, policies, settings..)? I am a little scared about this..

Thanks in advance!