Hello Mayki !

Sorry, but the guest can't use Messenger - it's impossible to identify whom to respond.

Thank you for your answer LeonidS 

FYI: on old Dolphin site we used third-party chat called Comet Chat which has the option for Dolphin integration and the ability to open chat to non registered users. It has it's own database tabel for "visitors" so it was possible to know to whom to respond aka visitor-001, vistor-002 etc.

Kind regards
Mayki