Chargement image lazy-loading (js)
http://www.blogduwebdesign.com/javascript-chargement/accelerer-chargement-site-lazy-loading/1122
base email responsive (audrey)
guide css 2017 https://www.campaignmonitor.com/css/media-queries/media/
templates gratuits : https://www.codeur.com/blog/template-email-gratuit-html/
tailles ecrans : http://www.responsive-mind.fr/resolution-iphone-retina/