if you want your actors to be independent computation flows and they're in different coroutines or threads, then you need to arrange that the data source can not modify the data once it arrives at the destination, in order to be safe.

in a single threaded fully cooperative environment you could ensure this by implication of only one coroutine running at a time, removing data races, but retaining logical ones.

if you want to eradicate logical races, or have actual parallel computation, then the source data must be copied into the message, or the content of the message be wrapped in a lock or similar.

in almost all practical scenarios this means the data source copies data into messages.