in the past I used my own imap-server (dovecot), postfix, procmail, fetchmail and so, for my Emails. I'm not quite sure what Zimbra can do for me.
Zimbra can store my mails, addresses, calendars and so on on my server so it'll evailable for me world wide. That I understood. But Zimbra isn't an email-Server?

Do I still need to configure my email-server (dovecot, postfix, procmail, fetchmail) to send and receive emails? I have email accounts on gmx, gmail and others, how I use this with Zimbra?