You can pass specific manager addresses when forwarding for a specific protocol. By default the InetAddressAcl is also parsed. So the set of actual manager addresses is the trap blocks located in the acl file and the set of added targets. You can disable the InetAddressAcl parsing by calling the method setInetAddressAclUsed(false).
To enable trap forwarding you must start the trap forwarder.
If you have manager addresses in your set of targets that are also present in InetAddressAcl, or you have no InetAddressAcl activated but are targeting the local host, your manager will receive the trap twice. To prevent this, configure the SnmpTrapForwarder carefully. You can, for example, disable the setInetAddressAcl parsing by calling isInetAddressAclUsed(false).