Zimbra backups are performed LIVE, the server remains operational and accessible, this is a unique feature of Zimbra Network Edition. Zimbra Open Source Edition does not have the same backup/restore feature. The Zimbra full backup process places the account’s mailbox in maintenance mode to temporarily block mail delivery and user access to that mailbox. and Returns that account’s mailbox to active mode and moves on to the next one. For more details see the Zimbra Administration Guide.