Plesk 11.5 Email restore from Backup

[applic]

Hello.
I have a big problem.
I made a domaintransfer to another provider.
The problem is that my emailprogram (thunderbird) didn`t downloaded all emails from the old provider.

I need the emails from the old mailserver, but i cannot access the webmail in Plesk, because the domain is already transfered.

At my new provider, i do not have plesk, so i cannot use the old backup =(

Is there a way to get my old emails from the Plesk Backup file?
Or to access "Webmail" without a domain?

I hope you have a solution for me.

regards

Daniel