It would be ideal to solve this issue in asyncore.py by fixing dispatcher.accept() once and for all, but I'm not sure whether this can be done in a fully retro-compatible way in terms of asyncore API.

Alternatively SMTPServer.handle_accept() can be fixed in the same way as pyftpdlib did:
http://code.google.com/p/pyftpdlib/source/browse/tags/release-0.5.2/pyftpdlib/ftpserver.py#622

   def handle_accept(self)
       try:
            sock, addr = self.accept()
        except TypeError:
            # sometimes accept() might return None
            return
        except socket.error, err:
            # ECONNABORTED might be thrown
            if err[0] != errno.ECONNABORTED:
                raise
            return
        else:
            # sometimes addr == None instead of (ip, port)
            if addr == None:
                return