I was running OS 10.13.6. I made a clone of my MacBook Pro using Super Duper. I installed Big Sur. I went to open my mailboxes and all my hundreds of mailboxes are there - but they are all EMPTY! How do I restore the mailboxes?
Back up your Mac.
Rebuild Mailboxes.
Mail > Mailboxes > Rebuild
Ref:
https://support.apple.com/guide/mail/rebuild-mailboxes-mlhlp1227/mac
Back up your Mac.
Rebuild Mailboxes.
Mail > Mailboxes > Rebuild
Ref:
https://support.apple.com/guide/mail/rebuild-mailboxes-mlhlp1227/mac
Recover Missing Mailboxes After Big Sur Update
