In the instructions for creating an address we only mention two routing types "Multicast" and "Anycast" but the dropdown also has a "Both" option, not sure what this really means from a routing perspective but if it's there it should be mentioned.

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6.4. Managing Addresses and Queues
6.4.1. Creating Addresses
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Routing type

Select one of the following options:

Multicast - Messages sent to this address will be distributed to all subscribers.
Anycast - Messages sent to this address will be distributed to only one subscriber.
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If you select "Both" the address is created with delivery modes MULTICAST and ANYCAST so I suspect the distribution will also depend on some other factor.