To use programs like Windows Mail, Outlook or Thunderbird with your university email you need to set up the outgoing mail server (SMTP)
Address: smtpserv.uni-tuebingen.de, Port 587, Encryption: STARTTLS
Through autentification with your university username and password you can then send university email from our network.
If you use the standard SMTP settings on your mail program, you will probably not be able to send emails from your university email address.
This post is also available in de_DE.