In which database objects are maintainer references ("mnt-by") mandatory?

t is mandatory to include an "mnt-by" reference to a maintainer (mntner) object in the following object types: person, mntner, role, as-block, as-set, aut-num, domain, filter-set, inet6num, inetnum, inet-rtr, irt, key-cert, organisation, peering-set, poem, poetic-form, route, route6, route-set, rtr-set.

For more information about RIPE Database object types, please see the RIPE Database Reference Manual.