In a recient post by the Gmail team that announced a new option for users. Something that should make established contacts very happy. IMAGES ON for CONTACTS… That is right Gmail will be enabling images for users that have sent at least two emails to the sender of the inbound email, and only if your authenticating. It almost makes you want to remove that DONOTREPLY@ option from your emails and ask for customer feedback via email.
As a safety option, Gmail also provides the option to disable images from your contacts (think about the friends that send you those NSFW forwards – yeah you know who you are) so your not auto loading images from that specific individual – to do so (this works for anyone you have previously allowed all images from too) , click “Don’t display from now on” under the “Show details” link of an email from them with images. or to make this a global setting, select “Ask before displaying external content” under “External content” on the general Settings tab.
Gmail uses SPF and DKIM to authenticate inbound emails – so if your not doing this now I’d recomend you get working on these technologies.