You can just plug in a cheap USB Ethernet adapter and have the same functionality with this.
With what USB port? It only has the micro-USB charging port that can be converted to USB-host with the appropriate adapter. Go ahead and look up the full specs, they're not even mentioned in TFA.
... They're bought as servers and media players. For that purpose, this alternative should be quite suitable
Without a LAN port? Good luck.
Sendmail may be safely run set-user-id to root. -- Eric Allman, "Sendmail Installation Guide"