Step Wise Manual T-online mail settings for thunderbird
If you don't have a T-online mail address. you can create an email id from here then you can T-online 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, T-online Email address and Password then press Continue.
Click on the Manual config menu at bottom.
Enter Below T-online incoming server settings.
In incoming click on the dropdown menu and select IMAP.
Add server host :secureimap.t-online.de
Port: 993
select SSL/TLS
Enter Below T-online outgoing server settings.
In outgoing select SMTP.
Add server host :securesmtp.t-online.de
Port: 465
select SSL/TLS
Tap on Done. Now you are ready to use your T-online email account on your Thunderbird.