If you don't have a Oi mail address. you can create an email id from here then you can Oi 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, Oi Email address and Password then press Continue.
Click on the Manual config menu at bottom.
Enter Below Oi incoming server settings.
In incoming click on the dropdown menu and select POP.
Add server host :pop3.oi.com.br
Port: 110
select SSL/TLS
Enter Below Oi outgoing server settings.
In outgoing select SMTP.
Add server host :smtp.oi.com.br
Port: 25
select SSL/TLS
Tap on Done. Now you are ready to use your Oi email account on your Thunderbird.