Vacation message and forwarder can be set by clicking the option "Auto Response" on top of web mail main page.
Do not forward your message to an outside email address and stop reading/deleting message locally. This will fill your quota and account will be locked.
The following figure 1.2.9 highlights the required options to enable forwarding and vacation message.
Read the status message (displayed in green) after committing the changes.
Auto response and message forwarding