A network interface device includes a host interface for connection to a host processor having a memory. A network interface is configured to transmit and receive data packets over a data network, which supports multiple tenant networks overlaid on the data network. Processing circuitry is configured to receive, via the host interface, a work item submitted by a virtual machine running on the host processor, and to identify, responsively to the work item, a tenant network over which the virtual machine is authorized to communicate, wherein the work item specifies a message to be sent to a tenant destination address. The processing circuitry generates, in response to the work item, a data packet containing an encapsulation header that is associated with the tenant network, and to transmit the data packet over the data network to at least one data network address corresponding to the specified tenant destination address.