1. Log into your Roundcube mail provider. 

Eg : webmail.domain.com

2. When you are successfully logged in, go to Settings.

3. In the settings menu, select Filters, you create a new filter on the bottom of the filter.

4. For incoming mail: select All messages

      Dropdown menu: In the dropdown menu select Reply with message

      Message body: Please type the message you want to send send on the out of office reply.

5. To enable and save this filter, UNTICK the Filter Disabled box. This will make the out of office reply enabled.

6. After this is done press Save. Your out of office is now enabled and working.