A group communication mechanism for optimized reliable non-member group communication through write-only membership is disclosed. The group communication mechanism comprises two or more group member processes that receive all messages that are sent to a group. The group communication mechanism further comprises a non-group member process that has a "write-only" group membership status and does not receive any messages that are sent to the group. The non-group member process is configured to send (a) one or more messages to the group, and (b) in connection with each message that it sends to the group, a different sequence value. Each sequence value identifies an order of a message relative to other messages that the non-group member process sends to the group.