The trial version of CodeTwo Exchange Migration works for 30 days for an unlimited number of mailboxes. When the 30 days are over, the software will cease to work - it needs to be activated with a purchased license key.
Although there are no mailbox number limitations during the 30-day trial period, you will be eligible to migrate up to ten single items in every Outlook type of folder including public folders. It means that if you have, e.g., 12 items in the inbox of the particular mailbox, only 10 of them will be migrated. To have the rest of items migrated after activating the program to the full version, use the rescan feature that will examine the content of all copied folders from the source mailboxes in search for new items and migrate them.
Activation - this article describes the activation procedure of the program.