ThunderBird

When adding an account use a custom manual account associated wth your sso account.

Configure Manually during Account setuo

IMAP
Server: 3gy.de
Port: 993
Conn type etc dropdown select secure
AuthType: Normal Password
Accountname: reggeduser

SMPT
Server: 3gy.de
Port: 465
Conn type etc dropdown select secure
AuthType: Normal Password
Accountname: reggeduser

IMAP

Port: 993