Access the following link [only in german]:
Log in with your weißensee eMail address and your eMail password.
(>>>> analogous to the absence note, the password can be changed via the "Passwort" tab!<<)
Click on the "Autoresponder" tab
Then click on "active", enter your text,
enter a start and end date below and click on "Apply changes" [Änderungen übernehmen].