Accessing Gmail From Terminal
I'm sure that by "access my Gmail smtp account just using the terminal" you mean "Using a command line program in the terminal" :) 

I personally don't use Mutt and don't know the program. However, it is one of the best command line email client. 

Everything seems to be well explained on the webpage you provide via the link

I'm using alpine (same concept). Here is a tuto: How to set Alpine and gmail