Smart Mail gives account holders the ability to set up filters which respond to incoming mail, through Roundcube filtering.
This includes the ability to autorespond to all emails with a defined response as is the case with Out Of Office notices.
Navigate to the Webmail interface at https://webmail.smartmail.email
Login using your email address (as username) and email account password
Click on the Settings icon in the top right of your Roundcube Mail screen
Click on the Filters item in the Settings menu
Either select from an item in the Filter Sets listing (if there are items) or click the Plus icon at the bottom of the listing area
If managesieve is in the Filter Set you should use that
From there you can create any filter and activate
There may already be a Vacation filter available, if so you can edit that
It is likely that it will be slightly greyed out to indicate that it is not active.
You can create an unlimited number of filters using the same method.
If setting up filters that deal with spam, you should not bounce the emails - it only compounds the problem of email traffic
Spammers are not concerned with bounces - the bounce may even bounce right back to you again.
Delete the emails or send them to junk depending on how sure you are that you are catching real spam or other unwanted emails