I'm testing the open source version of Zimbra, I've worked on user migration/mailbox migration. I created a little over 9000 accounts, and receive a notice when trying to view the accounts "The number of results to be displayed is over the limit. Please use search to refine the results". Using different search strings do display the accounts.
My question is, if I can raise this limit. I didn't troubleshoot to find the exact number that trips this off, but one of my search criteria returned 3000 results, and that worked fine.