In last blog we already talking about Migrate Zimbra from 32bit to 64bit , however Zmmailbox is quite slow when export and import when you have greate many mailboxes. Each mailbox will cost 5 second, so when you have for example more than 10000 account, that would be a disaster. In Zimbra official documentation, it also mentioned, when migrate 30GB data, will cost 5 days and night.

There would be a few ways to accelerate the speed, but it always be a good idea to find out how many data you are facing. The empty mailbox you wont need to migrate mailbox. That’s why we can create a script to find out the list of non-empty mailbox account.