For unmappedSourcePolicy = ReportingPolicy.WARN or above, one can use @BeanMapping(ignoreUnmappedSourceProperties = {...}) to declare source properties which are omitted intentionally. However, an equally simple dual option is missing. I'd suggest having a ignoredSourcePolicy configuration which warns / fails if an unknown source property is missing. This is useful for keeping this list "in sync" with reality, especially helpful after refractoring.

I am aware that one could achieve through ignoreByDefault = true, but then you'd have to write all mappings explicitly.

Sure, compared to a required missing target property, an ignored missing source property is not really dramatic, but it helps with debugging and keeping code clean. Its definitely a low-priority suggestion.