Assuming you are running a recent version of Postfix, yes!

Because Zimbra itself runs on Postfix, one of the most scalable, proven email server technologies in the world, migrating from any other Postfix server is made easier. Among others, options include being able to migrate just some mailboxes, as you need, over an extended period of time. These options generally apply to both the 01.com shared hosting environment, to dedicated servers hosted with 01.com, and also to Zimbra servers we may help you install and to which you migrate at your own office or data center. Please contact us for more information about Postfix to Zimbra migrations.