Why A mesh network is a data network in which each node routes traffic for its neighbors, forming a self-healing web of links. Amateur mesh systems such as AREDN and HSMM-Mesh run standard TCP/IP networking over Wi-Fi hardware retuned to ham bands, so every node is identified by an Internet Protocol address just like any computer on a LAN. Routing protocols then use those addresses to find the best path through the mesh.
Watch out Talk groups belong to DMR digital voice systems, where they select which conversation a repeater carries; they are not network node addresses. Email addresses and trust servers relate to other services (Winlink uses a trust/authentication concept), not to mesh node identification.
Mesh = a ham-band computer network, so nodes get IP addresses, just like any router on the Internet.