transferring email folders

Just a guess, but my guess is you did not follow the steps in Setup Assistant and Migration Assistant and use some other method to execute Migration Assistant. If that is correct, I would recommend doing an erase and then re-doing Setup Assistant. If your old Mac did not have a Time Machine backup, then create one! You will need an External Hard Disk ( I'd suggest a OWC Mercury Elite Pro ) and follow the directions Apple explains in Back up your Mac with Time Machine.

Well you have NOT read the link provided, here it is again. Your networks security has nothing to do with your problem, please actually read the information in the link and you will understand.

Setup Assistant and Migration Assistant

I'm telling you to use the Time Machine method, using the direct connect method is not as reliable and is expensive. If you follow the advice provided your migration will work just fine. It has for millions of users before you. However of course it is your call which method you want to use.

Great, before you do on the MBA please ensure any third party apps you want to migrate are 64 bit apps. Only 64 bit apps will run on Mac OS Big Sur and later. If you are unsure which of your apps are 32 or 64 bit apps, please research using a tool such as Roaring Apps. You can also use the System Information tool built into your MBA to inventory each app and it will tell you if the apps are 32 bit or 64 bit. If you find you have some third party 32 bit apps that you want to migrate you will need to upgrade or replace them before you do your migration.

Your welcome. If you feel this thread has been answered please indicate that. Doing so may help another user.

If you read the document, Setup Assistant and Migration Assistant, you’ll see you should never use Wi-Fi to migrate.

Never Ever use Wi-Fi for SA or MA!!!!!!!!!!!!!!!!!!!