Product\ProductGateway.If you want to register it under different name for example "productGateway", then pass it to annotation
Gatewayenables method to be used as Messaging Gateway. You may have multiple Gateways defined within interface.
replyChannelwhich contains automatically created Channel. During Endpoint's method invocation, if any value was returned it will be sent via reply Channel. This way gateway may receive the reply and return it.
$contentparameter to message payload
$contentto message's payload and will add to headers under "receiverEmail" key value of