You have reviewed the articles Configuring Kerio Anti-Spam and Kerio Connect Anti-Spam Filters and would like to know if it is okay to have every email be checked against the Spam URI Realtime Blocklist (SURBL).
SURBLs are lists of websites that have appeared in unsolicited messages. Unlike most lists, SURBLs are not lists of message senders.
It is a good idea to leave this enabled in Configuration > Spam Filter > Kerio Anti-Spam
If an email contains a link to a website that has appeared in confirmed spam messages and therefore got listed in the SURBL database, such email would be considered as likely a spam and an appropriate score would be added to it.
#2430154 is a relevant ticket that may be reviewed for more details.