For e-mail migration optimization you can request Microsoft to disable the default Throttling policy for a specific period. During that time throughput will be maximized.
Global Admin credentials for the customer tenant
Log into the Microsoft Admin Portal using the Global Admin credentials of the customer tenant
Click on 'Need help and search'
Type 'EWS' in the search bar
Choose 'Increase EWS Throttling Policy'
Here you should get the option to run the automated test mentioned and disable the throttling policy for a specified period
Changing EWS throttling settings
Please run our automated test which will allow you to modify the EWS throttling policy for the duration of your migration. Note that even after this is run, EWS imports will still be limited to 150mb per 5 minutes per mailbox; to achieve higher migration throughput speeds, please migrate more users concurrently.
Please note that EWS throttling policy changes have no effect on the following migration types (using Microsoft tools): Hybrid, Cutover/Staged (RPC/HTTP), IMAP, G Suite, Public Folder or PST Import Service.