A catch-all address receives emails sent to non-existent addresses of your domain.
Example: If you set up a catch-all address for mydomain.at, emails sent to addresses like doesnotexist@mydomain.at or test123@mydomain.at will also be delivered.
Log in to CloudPit and open the desired web hosting package.
Open the Email section (1) and then switch to Catch-All (2).
Click Actions for the desired domain and select Change to Forwarding (3).

Select the mailbox to which emails sent to non-existent addresses should be delivered and save the change.
From now on, emails sent to non-existent addresses of this domain will be delivered to the selected mailbox.
In the Control Panel, open Web Hosting → Email Addresses (1).
Open the section Add New Email Address (2).
Enter the asterisk symbol * (3) in the Email Address field and select the desired domain after the @ symbol.

Then select the mailbox to which the emails should be delivered.
Click Add to create the catch-all address.
A catch-all address looks like this, for example:
*@mydomain.at