EdbMails offers a user-friendly solution by supporting parallel migration for up to 20 mailboxes. This tool can be effortlessly installed on multiple mailboxes, streamlining the migration process for different sets of mailboxes. It's worth noting that this approach doesn't rigidly restrict mailbox size or migration speed. Keep in mind that specific limitations from your Exchange Server could apply. Several environmental factors can affect migration speed, including internet connection quality, potential restrictions from local routers, constraints imposed by source and target servers, as well as the overall performance of the devices involved. An added advantage of EdbMails is its ability to automatically handle Exchange migration throttling. For comprehensive insights and effective strategies regarding your Exchange Server's migration limits, both in terms of size and speed, refer to the below links: