Gmail – Print emails from a specific person in Gmail

James Ferreira wrote a Chrome App for that and used Google Apps Script for it:

Gmail Print All PRO

• Google Apps Script Examples
• Chrome Web Store

Gmail Print All Pro is here to help you quickly export messages right to a Google Doc that you can print, save as a pdf, share with others, or store in a way that works for you. Built to be simple to use, all you do is add messages to a Gmail label and run Print All from your Chrome Web Apps screen. This will create a Document in Google Drive containing the content from your messages and you can even choose to have the attachments saved in the same folder.

It used to be free a charge, but nowadays a little fee is required. Program is said to have 22000 weekly users.

Note: I'm not affiliated to Gmail Print All PRO

The best and simple way is just select the part of the message you want to print, then right click and select print.