Start Thunderbird
From the menu choose "Tools" > "Accounts"
Verify the following settings:
Account Name:
Account Name (Example: E-Mail Account Felix Muster or the e-mail address)
Your Name:
Your first name and surname (lower- and/or uppercase)
E-mail Address:
Your Bluewin e-mail address
Choose "Server settings"
The "Server" field must contain pop.bluewin.ch
In the "User name" box, enter your user name (e-mail address without @bluewin.ch)
Click on "Outgoing Server (SMTP)"
Select "Edit"
The "Description" and "Server" fields must contain smtpauth.bluewin.ch
Type the number 587 into the "Port" field
Click "OK", then click "OK" again