If you don't have a I mail address. you can create an email id from here then you can I email login.
Open Thunderbird Software App. Click on Email
When you click on the email, pop-up Set UP an Existing Account Screen.
Enter Your name, I Email address and Password then press Continue.
Click on the Manual config menu at bottom.
Enter Below I incoming server settings.
In incoming click on the dropdown menu and select IMAP.
Add server host :imap.softbank.jp
Port: 993
select SSL/TLS
Enter Below I outgoing server settings.
In outgoing select SMTP.
Add server host :smtp.softbank.jp
Port: 465
select SSL/TLS
Tap on Done. Now you are ready to use your I email account on your Thunderbird.