# One-Way Communication Using an Empty GCOS

You can prevent contact between users, but you can also allow them to receive certain kinds of messages, using an empty GCOS. For example, you probably want to notify all users before a system shutdown. The empty GCOS is one that is assigned a name and number but no groups.

To enable this one-way communication, the originating (or sending) mailbox must have an FCOS that allows it to make messages and also allows the mailbox owner to make or give (messages) to a mailbox with an empty GCOS. The FCOS feature bits to accomplish this are:

- 020 (Make messages)

- 126 (Make/give to mailbox with empty GCOS)

The receiving mailbox must also have an FCOS that allows it to receive messages from other users (FCOS bit 040). These features enable a user to make a message, as well as give messages from other users, to the mailbox with the empty GCOS.

For example, suppose the local phone company notifies an answering service that maintenance on buried phone cables will disrupt service for two hours next week. If all customers have mailboxes with the FCOS and empty GCOS just described, and if the system administrator’s mailbox has the same FCOS, then the system administrator can use one-way communication to notify users in advance of the system shut down.

To use an empty GCOS and feature bits to enable one-way communication from one set of mailboxes to another:

1. Customize an FCOS to assign to the originating mailbox (the mailbox that sends the one-way messages), that includes the following feature bits:

   - 020 (Make messages)

   - 126 (Make/give to mailbox with empty GCOS)

2. Customize the FCOS assigned to the receiving mailbox to include feature bit 040 (Receive messages from other users).

3. Assign an empty GCOS to the receiving mailbox.