The accept router has no private options of its own. Unless it is being used purely for verification (see verify_only) a transport is required to be defined by the generic transport option. If the preconditions that are specified by generic options are met, the router accepts the address and queues it for the given transport. The most common use of this router is for setting up deliveries to local mailboxes. For example:

localusers:
  driver = accept
  domains = mydomain.example
  check_local_user
  transport = local_delivery

The domains condition in this example checks the domain of the address, and check_local_user checks that the local part is the login of a local user. When both preconditions are met, the accept router runs, and queues the address for the local_delivery transport.