According to our system, the mailbox info is 10.38 MB as of 26.05.2023 15:01, and our diagnostic tool says the same. I cannot access the mailbox to see what e-mails are there, but it shouldn’t be empty.
if your previous host is still active, you can use our automatic e-mail migration tool. If not, you have to connect and import the e-mail using an e-mail client, our WebMail doesn’t support importing too many e-mails at once.
No, that doesn’t do anything for your e-mails. You need to use an e-mail client. Do you use Outlook or some similar software? If not, I would suggest installing Thunderbird and importing your mail for example according to this external article.