In the following Received: email header, what does the IP address $64\mathrm{.}191\mathrm{.}152\mathrm{.}28$ show us$?$

Received: from

beniamin.hostguardian.com

$([64\mathrm{.}191\mathrm{.}152\mathrm{.}28]$:$56279)$

a$.$ The website advertised in the email message

b$.$ The IP Address of the mail server

c$.$ The address of the computer reading the emai

d$.$ The IP address of the sender$\text{'}$s computer