What is your primary concern before initiating a mailbox migration?

When it comes to such operations, every user thinks about particular migration rules and guidelines.

My main concerns are usually the following:

Does it allow me to use mapping or create all accounts manually (especially for 200+ accounts)?
Does it preserve folder structures or mix everything in one mailbox?
Can I schedule it to migrate during off-peak hours to avoid throttling?
Can I launch it multiple times to ensure new messages are migrated without duplicates?
The last point is critical, as once the migration is done, emails keep coming in. It means that if you resubmit the migration, it should not make copies of the messages already transferred. With that said, I have had situations where the migration tooling failed me and had to re-run the process to get the updated data. This option is only available in solutions that offer incremental migration.

Another critical feature is the ability to see what messages were successfully migrated and what migration tooling failed. The last thing anyone wants is to launch a migration process only to realize afterward that nothing was moved due to errors. Kernel Email Migrator checks all the boxes, including automatic and CSV-based mailbox mapping, off-peak scheduling, incremental migration, message filtering, pausing, migration reports in CSV format, and much more. It handles PST/OST/EML/MSG to Office 365 and IMAP-to-IMAP migrations with ease and provides a 15-day free trial to see how the tool works.

But what about you? What is your primary concern before migrating email?
https://www.nucleustechnologies.com/email-migrator/