+===============================
+Communicating without Mailboxes
+===============================
+
+Sometimes you don't want to simulate communications between actors as
+allowed by mailboxes, but you want to create a direct communication
+between two arbitrary hosts. This can arise when you write a
+high-level model of a centralized scheduler, or when you model direct
+communications such as one-sided communications in MPI or remote
+memory direct access in PGAS.
+
+For that, :cpp:func:`Comm::sendto() <simgrid::s4u::Comm::sendto()>`
+simulates a direct communication between the two specified hosts. No
+mailbox is used, and there is no rendezvous between actors. You can
+freely mix such direct communications and rendezvous-based
+communications. Alternatively, :cpp:func:`Comm::sendto_init()
+<simgrid::s4u::Comm::sendto_init()>` and
+:cpp:func:`Comm::sendto_async() <simgrid::s4u::Comm::sendto_async()>`
+create asynchronous direct communications.
+