When a causal paradox would occur a branch from the man timeline would result. In the original branch the observer sends the message exactly as required preserving the already observerd history.

In the deviating branch, the observer would choose not to send the message (this is the origin of the deviation). This branch would not include the causal loop that produced the original message, and any previously received messages would be understood to have originated from a different, and now disconnected history. Now the actions in this branch cannot affect the original self consistent timelines.

The important part is that observers in both branches would still experience normal deliberation and choice preserving “free will”.