To aid you in troubleshooting your issue can you supply additional information on your current rule configurations.

1. You stated user A,B and C can receive each others messages. When a message is received by User A does it Get forwarded to user B and C?

2. Do usres B and C have rules created to forward to user A?

3. When a messages is sent to User A, and forwards to user B and C, do these messages get sent back to user A or remain in User A's inbox?

4. Confirm the OOA is not configured on user B and C Outlook client.

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