Re: Am i being thick...
The email server will add your external IP address to the email header, which will give them the public wi-fi from the ISP.
Emails clients will either add the local IP to the email header or send it in the helo to the email server which will then add it the header. (webmail won't include it as you can't get the local IP in a browser)
The MAC address will be in the log of the wi-fi networks DHCP or maybe still in the DHCP server with the IP lease. Which will also includes the host name of the device. Windows 7 and maybe 8 would name PCs after the initial user so you get a lot of first names. Android and Windows 10 gives seemingly random names.
My home router (ISP provided) still lists the MAC address of a device which was connected once over 3 months ago, includes the host name (first name of the owner) so I know what device it was.