Map the complete forwarding path
Write down the original mailbox, every forwarding destination, and any aliases or rules that apply along the way. A destination may itself forward to the source mailbox, directly or through another address, creating a cycle that is not obvious from a single setting. Review the rules at each address involved rather than checking only the first mailbox.
Keep the route simple when possible. If several people need the same messages, consider whether a shared destination or a deliberate distribution address is more appropriate than chaining multiple forwards. Do not add a second rule until you know how the first destination handles incoming messages.
Test with a message and revisit after changes
After configuring forwarding, send a message from an external address and verify where it arrives. Check both the intended destination and the original mailbox, and look for repeated copies or delayed delivery. A successful save does not prove that the complete route behaves as intended.
Recheck the forwarding path whenever an address, alias, or mailbox rule changes. A route that was safe before can become circular when a destination is later redirected back. If a loop is suspected, remove or disable the newest forwarding rule and trace the route before enabling it again.